C-Language Overview - Tutorial & Theory for Beginners

String standard functions

2012-01-17T06:56:00.004-08:00

Functions	Description
Strlen()	Determines the length of a string
Strcpy()	Copies a string from source to destination
Strncpy()	Copies characters of a string to another string up to the specified length
Stricmp()	Compares characters of two strings
Strcmp()	Compares characters of two strings up to the specified length
Strncmp()	Compares characters of two strings up to the specified length
Strnicmp()	Compares characters of two strings up to the specified length
Strlwr()	Converts uppercase characters of a string to lower case
Strupr()	Converts lowercase characters of a string to upper case
Strdup()	Duplicates a string
Strchr()	Determines the first occurrence of a given character in a string
Strrchr()	Determines the last occurrence of a given character in a string
Strstr()	Determines the first occurrence of a given string in another string
Strcat()	Appends source string to destination string
Strrev()	Reverses all characters of a string
Strset()	Sets all characters of a string with a given argument or symbol
Strspn()	Finds up to what length two strings are identical
Strpbrk()	Searches the first occurrence of the character in a given string and then displays the string starting from that character

sprintf()

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This function is similar to the printf() function except for a small difference between them. The printf() function sends the output to the screen whereas the sprint() function writes the values of any data type to an array of characters.

sscanf()

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This function allows reading characters from a character array and writes them to another array. This function is similar to scanf(), but instead of reading from standard input it reads data from an array.

Add Comments in C

2012-01-17T06:52:00.001-08:00

Load the file comments.c and observe it on your monitor for an example of how comments
can be added to a C program.

/* This is a comment ignored by the compiler */
main( ) /* This is another comment ignored by the compiler */
{
printf("We are looking at how comments are "); /* A comment is
allowed to be
continued on
another line */
2-3 C Tutorial Getting started in C
printf("used in C.\n");
}
/* One more comment for effect */

Comments are added to make a program more readable to you but the compiler must ignore the comments. The slash star combination is used inC for comment delimiters. They are illustrated in the program at hand. Please note that the program does not illustrate good commenting practice, but is intended to illustrate where comments can go in a program. It is a very sloppy looking program. The first slash star combination introduces the first comment and the star at the end of the first line terminates this comment. Note that this comment is prior to the beginning of the program illustrating that a comment can precede the program itself. Good programming practice would include a comment prior to the program with a short introductory description of the program. The next comment is after the "main( )" program entry point and prior to the opening brace for the program code itself. The third comment starts after the first executable statement and continue for four lines. This is perfectly legal because a comment can continue for as many lines as desired until it is terminated. Note carefully that if anything were included in the blank spaces to the left of the three
continuation lines of the comment, it would be part of the comment and would not be compiled. The last comment is located following the completion of the program, illustrating that comments can go nearly anywhere in a C program. Experiment with this program be adding comments in other places to see what will happen. Comment out one of the printf statements by putting comment delimiters both before and after it and see that it does not get printed out.
Comments are very important in any programming language because you will soon forget what you did and why you did it. It will be much easier to modify or fix a well commented program
a year from now than one with few or no comments. You will very quickly develop your own personal style of commenting.
Somecompilers allow you to "nest" comments which can be very handy if you need to "comment out" a section of code during debugging. Check your compiler documentation for the availability of this feature with your particular compiler. Compile and run comments.c at this time.

To Print Some Numbers

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Load the file named oneint.c and display it on the monitor for our first example of how to
work with data in a C program.

main( )

{

int index;

index = 13;

printf("The value of the index is %d\n",index);

index = 27;

printf("The valve of the index = %d\n",index);

index = 10;

printf("The value of the index = %d\n",index);

}

The entry point "main" should be clear to you by now as well as the beginning brace. The first
new thing we encounter is the line containing "int index;", which is used to define an integer
variable named "index". The "int" is a reserved word in C, and can therefore not be used for
anything else. It defines a variable that can have a value from -32768 to 32767 on most MS-DOS
microcomputer implementations of C. It defines a variable with a value from -2147483648 to
2147483647 in HiTech C. Consult your compiler users manual for the exact definition for your
compiler. The variable name, "index", can be any name that follows the rules for an identifier and is not one of the reserved words for C. Consult your manual for an exact definition of an
identifier for your compiler. In HiTech C, the construction of identifier names is the same as
in UNIX, however 31 characters and both cases are significant. The compiler prepends an
underscore to external references in the assembler pass. The final character on the line, the
semi-colon, is the statement terminator used in C.
We will see in a later chapter that additional integers could also be defined on the same line,
but we will not complicate the present situation.
Observing the main body of the program, you will notice that there are three statements that
assign a value to the variable "index", but only one at a time. The first one assigns the value of
13 to "index", and its value is printed out. (We will see how shortly.) Later, the value 27 is
assigned to "index", and finally 10 is assigned to it, each value being printed out. It should be
intuitively clear that "index" is indeed a variable and can store many different values. Please
note that many times the words "printed out" are used to mean "displayed on the monitor". You
will find that in many cases experienced programmers take this liberty, probably due to the
"printf" function being used for monitor display.

First C Program

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You are looking at the simplest possible C program. There is no way to simplify this program,
or to leave anything out. Unfortunately, the program doesn’t do anything.
main()
{}
The word "main" is very important, and must appear once, and only once, in every C program.
This is the point where execution is begun when the program is run. We will see later that this
does not have to be the first statement in the program, but it must exist as the entry point.
Following the "main" program name is a pair of parentheses, which are an indication to the
compiler that this is a function. We will cover exactly what a function is in due time. For now,
I suggest that you simply include the pair of parentheses.
The two curly brackets { }, properly called braces, are used to define the limits of the program
itself. The actual program statements go between the two braces and in this case, there are no
statements because the program does absolutely nothing. Youcan compile and run this program,
but since it has no executable statements, it does nothing. Keep in mind however, that it is a
valid C program.

List.xrel file

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This file will list the source files for you with line numbers and filename. To use it, simply type
"LIST" followed by the appropriate filename. Type list firstex.c now for an example.
The C source code is given later in Chapter 14 along with a brief description of its operation.
Applix 1616 users always have the inbuilt edit comand available to them, so this program
isn’t really essential.

What Is An Identifier

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Before you can do anything in any language, you must at least know how you name an identifier.
An indentifier is used for any variable, function, data definition, etc. In the programming language
C, an identifier is a combination of alphanumeric characters, the first being a letter of the
alphabet or an underline, and the remaining being any letter of the alphabet, any numeric digit,
or the underline. Two rules must be kept in mind when naming identifiers.
1. The case of alphabetic characters is significant. Using "INDEX" for a variable is not
the same as using "index" and neither of them is the same as using "InDex" for a variable. All
three refer to different variables.
2. As C is defined, up to eight significant characters can be used and will be considered
significant. If more than eight are used, they may be ignored by the compiler. This may or may
not be true of your compiler. You should check your reference manual to find out how many
characters are significant for your compiler. The HiTech C compiler used with the Applix 1616
allows 31 significant characters, and prepends an underscore (_)
It should be pointed out that some C compilers allow use of a dollar sign in an identifier name,
but since it is not universal, it will not be used anywhere in this tutorial. Check your documentation
to see if it is permissible for your particular compiler.

Difference between return 0 and exit(0)

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return 0 is used when a funtion has return type of int n we do not return any variable , where as exit(0) is used to terminate the program abruptly, it can take values in miliseconds.

return: control return to a function.

exit():Use to terminate a process.

File Handling in C Language

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In this section, we will discuss about files which are very important for storing information permanently. We store information in files for many purposes, like data processing by our programs.

What is a File?

Abstractly, a file is a collection of bytes stored on a secondary storage device, which is generally a disk of some kind. The collection of bytes may be interpreted, for example, as characters, words, lines, paragraphs and pages from a textual document; fields and records belonging to a database; or pixels from a graphical image. The meaning attached to a particular file is determined entirely by the data structures and operations used by a program to process the file. It is conceivable (and it sometimes happens) that a graphics file will be read and displayed by a program designed to process textual data. The result is that no meaningful output occurs (probably) and this is to be expected. A file is simply a machine decipherable storage media where programs and data are stored for machine usage.

Essentially there are two kinds of files that programmers deal with text files and binary files. These two classes of files will be discussed in the following sections.

ASCII Text files

A text file can be a stream of characters that a computer can process sequentially. It is not only processed sequentially but only in forward direction. For this reason a text file is usually opened for only one kind of operation (reading, writing, or appending) at any given time.

Similarly, since text files only process characters, they can only read or write data one character at a time. (In C Programming Language, Functions are provided that deal with lines of text, but these still essentially process data one character at a time.) A text stream in C is a special kind of file. Depending on the requirements of the operating system, newline characters may be converted to or from carriage-return/linefeed combinations depending on whether data is being written to, or read from, the file. Other character conversions may also occur to satisfy the storage requirements of the operating system. These translations occur transparently and they occur because the programmer has signalled the intention to process a text file.

Binary files

A binary file is no different to a text file. It is a collection of bytes. In C Programming Language a byte and a character are equivalent. Hence a binary file is also referred to as a character stream, but there are two essential differences.

No special processing of the data occurs and each byte of data is transferred to or from the disk unprocessed.
C Programming Language places no constructs on the file, and it may be read from, or written to, in any manner chosen by the programmer.

Binary files can be either processed sequentially or, depending on the needs of the application, they can be processed using random access techniques. In C Programming Language, processing a file using random access techniques involves moving the current file position to an appropriate place in the file before reading or writing data. This indicates a second characteristic of binary files.
They a generally processed using read and write operations simultaneously.

For example, a database file will be created and processed as a binary file. A record update operation will involve locating the appropriate record, reading the record into memory, modifying it in some way, and finally writing the record back to disk at its appropriate location in the file. These kinds of operations are common to many binary files, but are rarely found in applications that process text files.

Creating a file and output some data

In order to create files we have to learn about File I/O i.e. how to write data into a file and how to read data from a file. We will start this section with an example of writing data to a file. We begin as before with the include statement for stdio.h, then define some variables for use in the example including a rather strange looking new type.

/* Program to create a file and write some data the file */

#include <stdio.h>

#include <stdio.h>

main( )

{

     FILE *fp;

     char stuff[25];

     int index;

     fp = fopen("TENLINES.TXT","w"); /* open for writing */

     strcpy(stuff,"This is an example line.");

     for (index = 1; index <= 10; index++)

     	fprintf(fp,"%s Line number %d\n", stuff, index);

     fclose(fp); /* close the file before ending program */

}

The type FILE is used for a file variable and is defined in the stdio.h file. It is used to define a file pointer for use in file operations. Before we can write to a file, we must open it. What this really means is that we must tell the system that we want to write to a file and what the file name is. We do this with the fopen() function illustrated in the first line of the program. The file pointer, fp in our case, points to the file and two arguments are required in the parentheses, the file name first, followed by the file type.

The file name is any valid DOS file name, and can be expressed in upper or lower case letters, or even mixed if you so desire. It is enclosed in double quotes. For this example we have chosen the name TENLINES.TXT. This file should not exist on your disk at this time. If you have a file with this name, you should change its name or move it because when we execute this program, its contents will be erased. If you donâ€™t have a file by this name, that is good because we will create one and put some data into it. You are permitted to include a directory with the file name.The directory must, of course, be a valid directory otherwise an error will occur. Also, because of the way C handles literal strings, the directory separation character â€˜\â€™ must be written twice. For example, if the file is to be stored in the \PROJECTS sub directory then the file name should be entered as “\\PROJECTS\\TENLINES.TXT”. The second parameter is the file attribute and can be any of three letters, r, w, or a, and must be lower case.

Reading (r)

When an r is used, the file is opened for reading, a w is used to indicate a file to be used for writing, and an a indicates that you desire to append additional data to the data already in an existing file. Most C compilers have other file attributes available; check your Reference Manual for details. Using the r indicates that the file is assumed to be a text file. Opening a file for reading requires that the file already exist. If it does not exist, the file pointer will be set to NULL and can be checked by the program.

Here is a small program that reads a file and display its contents on screen.

/* Program to display the contents of a file on screen */

#include <stdio.h>

void main()

{

   FILE *fopen(), *fp;

   int c;

   fp = fopen("prog.c","r");

   c = getc(fp) ;

   while (c!= EOF)

   {

   		putchar(c);

		c = getc(fp);

   }

   fclose(fp);

}

Writing (w)

When a file is opened for writing, it will be created if it does not already exist and it will be reset if it does, resulting in the deletion of any data already there. Using the w indicates that the file is assumed to be a text file.

Here is the program to create a file and write some data into the file.

#include <stdio.h>

int main()

{

 FILE *fp;

 file = fopen("file.txt","w");

 /*Create a file and add text*/

 fprintf(fp,"%s","This is just an example :)"); /*writes data to the file*/

 fclose(fp); /*done!*/

 return 0;

}

Appending (a)

When a file is opened for appending, it will be created if it does not already exist and it will be initially empty. If it does exist, the data input point will be positioned at the end of the present data so that any new data will be added to any data that already exists in the file. Using the a indicates that the file is assumed to be a text file.

Here is a program that will add text to a file which already exists and there is some text in the file.

#include <stdio.h>

int main()

{

    FILE *fp

    file = fopen("file.txt","a");

    fprintf(fp,"%s","This is just an example :)"); /*append some text*/

    fclose(fp);

    return 0;

}

Outputting to the file

The job of actually outputting to the file is nearly identical to the outputting we have already done to the standard output device. The only real differences are the new function names and the addition of the file pointer as one of the function arguments. In the example program, fprintf replaces our familiar printf function name, and the file pointer defined earlier is the first argument within the parentheses. The remainder of the statement looks like, and in fact is identical to, the printf statement.

Closing a file

To close a file you simply use the function fclose with the file pointer in the parentheses. Actually, in this simple program, it is not necessary to close the file because the system will close all open files before returning to DOS, but it is good programming practice for you to close all files in spite of the fact that they will be closed automatically, because that would act as a reminder to you of what files are open at the end of each program.

You can open a file for writing, close it, and reopen it for reading, then close it, and open it again for appending, etc. Each time you open it, you could use the same file pointer, or you could use a different one. The file pointer is simply a tool that you use to point to a file and you decide what file it will point to. Compile and run this program. When you run it, you will not get any output to the monitor because it doesnâ€™t generate any. After running it, look at your directory for a file named TENLINES.TXT and type it; that is where your output will be. Compare the output with that specified in the program; they should agree! Do not erase the file named TENLINES.TXT yet; we will use it in
some of the other examples in this section.

Reading from a text file

#include <stdio.h>

Now for our first program that reads from a file. This program begins with the familiar include, some data definitions, and the file opening statement which should require no explanation except for the fact that an r is used here because we want to read it.

main( )

   {

     FILE *fp;

     char c;

     funny = fopen("TENLINES.TXT", "r");

     if (fp == NULL)

		printf("File doesn't exist\n");

     else {

      do {

       c = getc(fp); /* get one character from the file

       */

         putchar(c); /* display it on the monitor

       */

       } while (c != EOF); /* repeat until EOF (end of file)

     */

     }

    fclose(fp);

   }

In this program we check to see that the file exists, and if it does, we execute the main body of the program. If it doesn’t, we print a message and quit. If the file does not exist, the system will set the pointer equal to NULL which we can test. The main body of the program is one do while loop in which a single character is read from the file and output to the monitor until an EOF (end of file) is detected from the input file. The file is then closed and the program is terminated. At this point, we have the potential for one of the most common and most perplexing problems of programming in C. The variable returned from the getc function is a character, so we can use a char variable for this purpose. There is a problem that could develop here if we happened to use an unsigned char however, because C usually returns a minus one for an EOF – which an unsigned char type variable is not
capable of containing. An unsigned char type variable can only have the values of zero to 255, so it will return a 255 for a minus one in C. This is a very frustrating problem to try to find. The program can never find the EOF and will therefore never terminate the loop. This is easy to prevent: always have a char or int type variable for use in returning an EOF. There is another problem with this program but we will worry about it when we get to the next program and solve it with the one following that.

After you compile and run this program and are satisfied with the results, it would be a good exercise to change the name of TENLINES.TXT and run the program again to see that the NULL test actually works as stated. Be sure to change the name back because we are still not finished with TENLINES.TXT.

Array in C Language

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What is an Array in C Language?

An array in C Programing Language can be defined as number of memory locations, each of which can store the same data type and which can be references through the same variable name.

An array is a collective name given to a group of similar quantities. These similar quantities could be percentage marks of 100 students, number of chairs in home, or salaries of 300 employees or ages of 25 students. Thus an array is a collection of similar elements. These similar elements could be all integers or all floats or all characters etc. Usually, the array of characters is called a “string”, where as an array of integers or floats is called simply an array. All elements of any given array must be of the same type i.e we can’t have an array of 10 numbers, of which 5 are ints and 5 are floats.

Arrays and pointers have a special relationship as arrays use pointers to reference memory locations.

Declaration of an Array

Arrays must be declared before they can be used in the program. Standard array declaration is as

type variable_name[lengthofarray];

Here type specifies the variable type of the element which is going to be stored in the array. In C programmin language we can declare the array of any basic standard type which C language supports. For example

double height[10];
float width[20];
int min[9];
char name[20];

In C Language, arrays starts at position 0. The elements of the array occupy adjacent locations in memory. C Language treats the name of the array as if it were a pointer to the first element This is important in understanding how to do arithmetic with arrays. Any item in the array can be accessed through its index, and it can be accesed any where from with in the program. So

m=height[0];

variable m will have the value of first item of array height.

The program below will declare an array of five integers and print all the elements of the array.

int myArray [5] = {1,2,3,4,5};
/* To print all the elements of the array
for (int i=0;i<5;i++){
printf("%d", myArray[i]);
}

Initializing Arrays

Initializing of array is very simple in c programming. The initializing values are enclosed within the curly braces in the declaration and placed following an equal sign after the array name. Here is an example which declares and initializes an array of five elements of type int. Array can also be initialized after declaration. Look at the following C code which demonstrate the declaration andÂ initialization of an array.

int myArray[5] = {1, 2, 3, 4, 5}; //declare and initialize the array in one statement
int studentAge[4];
studentAge[0]=14;
studentAge[1]=13;
studentAge[2]=15;
studentAge[3]=16;

Performing operations on Arrays

Here is a program that will demonstrate the simple operations of the array.

#include <stdio.h>
void oneWay(void);
void anotherWay(void);
int main(void) {
printf("\noneWay:\n");
oneWay();
printf("\nantherWay:\n");
anotherWay();
}

/*Array initialized with aggregate */
void oneWay(void) {
int vect[10] = {1,2,3,4,5,6,7,8,9,0};
int i;
for (i=0; i<10; i++){
printf("i = %2d vect[i] = %2d\n", i, vect[i]);
}
}

/*Array initialized with loop */
void anotherWay(void) {
int vect[10];
int i;
for (i=0; i<10; i++)
vect[i] = i+1;
for (i=0; i<10; i++)
printf("i = %2d vect[i] = %2d\n", i, vect[i]);
}

/* The output of this program is
oneWay:
i = 0 vect[i] = 1
i = 1 vect[i] = 2
i = 2 vect[i] = 3
i = 3 vect[i] = 4
i = 4 vect[i] = 5
i = 5 vect[i] = 6
i = 6 vect[i] = 7
i = 7 vect[i] = 8
i = 8 vect[i] = 9
i = 9 vect[i] = 0

antherWay:
i = 0 vect[i] = 1
i = 1 vect[i] = 2
i = 2 vect[i] = 3
i = 3 vect[i] = 4
i = 4 vect[i] = 5
i = 5 vect[i] = 6
i = 6 vect[i] = 7
i = 7 vect[i] = 8
i = 8 vect[i] = 9
i = 9 vect[i] = 10
*/

Here is a more complex program that will demonstrate how to read, write and traverse the integer arrays

#include <stdio.h>
void intSwap(int *x, int *y);
int getIntArray(int a[], int nmax, int sentinel);
void printIntArray(int a[], int n);
void reverseIntArray(int a[], int n);

int main(void) {
int x[10];
int hmny;

hmny = getIntArray(x, 10, 0);
printf("The array was: \n");
printIntArray(x,hmny);
reverseIntArray(x,hmny);
printf("after reverse it is:\n");
printIntArray(x,hmny);
}

void intSwap(int *x, int *y)
/* It swaps the content of x and y */
{
int temp = *x;
*x = *y;
*y = temp;
}

/* n is the number of elements in the array a.
* These values are printed out, five per line. */
void printIntArray(int a[], int n){
int i;
for (i=0; i<n; ){
   printf("\t%d ", a[i++]);
   if (i%5==0)
   printf("\n");
}
printf("\n");
}

/* It reads up to nmax integers and stores then in a; sentinel
* terminates input. */
int getIntArray(int a[], int nmax, int sentinel)
{
int n = 0;
int temp;

do {
printf("Enter integer [%d to terminate] : ", sentinel);
scanf("%d", &temp);
if (temp==sentinel) break;
if (n==nmax)
printf("array is full\n");
else
a[n++] = temp;
}while (1);
return n;
}

/* It reverse the order of the first n elements of array */
void reverseIntArray(int a[], int n)
{
int i;
for(i=0;i<n/2;i++){
intSwap(&a[i],&a[n-i-1]);
}
}

Copy one array into another

There is no such statement in C language which can directly copy an array into another array. So we have to copy each item seperately into another array.

#include <stdio.h>
int main()
{
int iMarks[4];
short newMarks[4];
iMarks[0]=78;
iMarks[1]=64;
iMarks[2]=66;
iMarks[3]=74;
for(i=0; i<4; i++)
newMarks[i]=iMarks[i];
for(j=0; j<4; j++)
printf("%d\n", newMarks[j]);
return 0;
}

To summarize, arrays are provides a simple mechanism where more than one elements of same type are to be used. We can maintain, manipulate and store multiple elements of same type in one array variable and access them through index.

Multidimensional Arrays

In C Language one can have arrays of any dimensions. To understand the concept
of multidimensional arrays let us consider the following 4 X 5 matrix

Row number (i)

Column numbers (j)

0

11

3

5

-9

-6

1

5

6

-8

7

24

2

-8

9

2

12

45

3

10

13

-10

4

5

Let us assume the name of matrix is x

To access a particular element from the array we have to use two subscripts on for row number and other for column number the notation is of the form X [i] [j] where i stands for row subscripts and j stands for column subscripts. Thus X [0] [0] refers to 10, X [2] [1] refers to 16 and so on In short multi dimensional arrays are defined more or less in the same manner as single dimensional arrays, except that for subscripts you require two squire two square brackets. We will restrict our decision to two dimensional arrays.

Below given are some typical two-dimensional array definitions

float table [50] [50];
char line [24] [40];

The first example defines tables as a floating point array having 50 rows and 50 columns. the number of elements will be 2500 (50 X50).

The second declaration example establishes an array line of type character with 24 rows and 40 columns. The number of elements will be (24 X 40) 1920 consider the following two dimensional array definition int values [3] [4] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10. 11, 12, };

Values [0] [0] = 1 Values [0] [1] = 2 Values [0] [2] = 3 Values [0] [3] = 4
Values [1] [0] = 5 Values [1] [1] = 6 Values [1] [2] = 7 Values [1] [3] = 8
Values [2] [0] = 9 Values [2] [1] = 10 Values [2] [2] = 11 Values [2] [3] = 12

Here the first subscript stands for the row number and second one for column number. First subscript ranges from 0 to 2 and there are altogether 3 rows second one ranges from 0 to 3 and there are altogether 4 columns.

Alternatively the above definition can be defined and initialised as

int values [3] [4] = {
{
1, 2, 3, 4
}
{
5, 6, 7, 8
}
{
9, 10, 11, 12
}
};

Here the values in first pair of braces are initialised to elements of first row, the values of second pair of inner braces are assigned to second row and so on. Note that outer pair of curly braces is required. If there are two few values within a pair of braces the remaining elements will be assigned as zeros.

Here is a sample program that stores roll numbers and marks obtained by a student side by side in matrix

main ( )
{
int stud [4] [2];
int i, j;
for (i =0; i < =3; i ++)
{
printf ("\n Enter roll no. and marks");
scanf ("%d%d", &stud [i] [0], &stud [i] [1] );
}
for (i = 0; i < = 3; i ++)
printf ("\n %d %d", stud [i] [0], stud [i] [1]);
}

The above example illustrates how a two dimensional array can be read and how the values stored in the array can be displayed on screen.

What is a dangling pointer

2011-05-08T11:04:00.001-07:00

A dangling pointer arises when you use the address of an object after its lifetime is over. This
may occur in situations like returning addresses of the automatic variables from a function or
using the address of the memory block after it is freed.

How to write a C program

2011-05-08T11:01:00.003-07:00

We specified the algorithm using English statements. However, these statements are sufficiently ‘computer-oriented’ for a computer program to be written directly from them. Before we do this, let us see how we expect the program to work from the user’s point of view.

First, the program will type the request for the length of a side; we say the program prompts the user to supply data. The screen display might look like this:

Enter length of side:

The computer will then wait for the user to type the length. Suppose the user types 12. The display will look like this:

Enter length of side: 12

The program will then accept (we say read) the number typed, calculate the area and print the result. The display may look like this:

Enter length of side: 12

Area of square is 144

Here we have specified what the output of the program should look like. For instance, there is a blank line between the prompt line and the line that gives the answer; we have also specified the exact form of the answer. This is a simple example of output design. This is necessary since the programmer cannot write the program unless he knows the precise output required.

In order to write the computer program from the algorithm, a suitable programming language must be chosen. We can think of a program as a set of instructions, written in a programming language, which, when executed, will produce a solution to a given problem or perform some specified task.

The major difference between an algorithm and a program is that an algorithm can be written using informal language without having to follow any special rules (though some conventions are usually followed) whereas a program is written in a programming language and must follow all the rules (the syntax rules) of the language. (Similarly, if we wish to write correct English, we must follow the syntax rules of the English language).

In this series, we will be showing you how to write programs in C, the programming language developed by Ken Thompson and Dennis Ritchie of Bell Laboratories, and one of the most popular and widely used today. A program written in a high-level language such as C is usually referred to as a source program or source code.

The C program which requests the user to enter the length of a side and prints the area of the square is shown here:

#include main() { int a, s; printf("Enter length of side: "); scanf("%d", &s); //store length in s a = s * s; //calculate area; store in a printf("\nArea of square is %d\n", a); }

It is not too important that you understand everything about this program at this time. But you can observe that a C program has something (a function) called main followed by opening and closing brackets. Between the left brace { and the right brace } we have what is called the body of the function. The statement

int a, s;

is called a declaration. The parts of a line after double slashes ( // )are comments which help to explain the program but have no effect when the program is run. The asterisk ( * ) is used to denote multiplication.

All of these terms will be explained in detail in due course.

Develop the Algorithm

2011-05-08T11:01:00.001-07:00

Develop the Algorithm

Using the notion of an algorithm and the concept of a variable, we develop the following algorithm for calculating the area of a square, given one side:

Algorithm for calculating area of square, given one side

(1) Ask the user for the length of a side

(2) Store the value in the box s

(3) Calculate the area of the square (s times s)

(4) Store the area in the box a

(5) Print the value in box a, appropriately labelled

(6) Stop

When an algorithm is developed, it must be checked to make sure that it is doing its intended job correctly. We can test an algorithm by ‘playing computer,' that is, we execute the instructions by hand, using appropriate data values. This process is called dry running or desk checking the algorithm. It is used to pinpoint any errors in logic before the computer program is actually written. We should never start to write programming code unless we are confident that the algorithm is correct. Here, the algorithm is fairly simple, so it is easy to check that it is indeed correct.

Data and Variables

2011-05-08T11:00:00.000-07:00

All computer programs, except the most trivial, are written to operate on data. For example:

• the data for an action game might be keys pressed or the position of the cursor when the mouse is clicked;

• the data for a word processing program are the keys pressed while you are typing a letter;

• the data for an accounting program would include, among other things, expenses and income;

• the data for a program that teaches Spanish could be an English word that you type in response to a question.

For a program to be run, it must be stored in the computer’s memory. When data is supplied to a program, that data is also stored in memory. Thus we think of memory as a place for holding programs and data. One of the nice things about programming in a high-level language (like C or Java) is that you don’t have to worry about which memory locations are used to store your data. But how do we refer to an item of data, given that there may be many data items in memory?

Think of memory as a set of boxes (or storage locations). Each box can hold one item of data, for example, one number. We can give a name to a box, and we will be able to refer to that box by the given name. In our example, we will need two boxes, one to hold the side of the square and one to hold the area. We will call these boxes s and a, respectively.

If we wish, we can change the value in a box at any time; since the values can vary, s and a are called variable names, or simply variables. Thus a variable is a name associated with a particular memory location or, if you wish, it is a label for the memory location. We can speak of giving a variable a value, or setting a variable to a specific value, such as 1, for instance. Important points to remember are:

• a box can hold only one value at a time; if we put in a new value, the old one is lost;

• we must not assume that a box contains any value unless we specifically store a value in the box. In particular, we must not assume that the box contains 0.

Variables are a common feature of computer programs. It is very difficult to imagine what programming would be like without them. In everyday life, we often use variables. For example, we speak of an ‘address’. Here, ‘address’ is a variable whose value depends on the person under consideration. Other common variables are telephone number, name of school, subject, size of population, type of car, television model, etc. (What are some possible values of these variables?)

Now that we know a little bit about variables, we are ready to develop the algorithm for calculating the area of a square.

Write an algorithm to solve the problem

2011-05-08T10:59:00.001-07:00

An algorithm is a set of instructions which, if faithfully followed, will produce a solution to a given problem or perform some specified task. When an instruction is followed, we say it is executed. We can speak of an algorithm for finding a word in a dictionary, for changing a punctured tyre or for playing a video game.

For any problem, there will normally be more than one algorithm to solve it. Each algorithm will have its own advantages and disadvantages. When we are searching for a word in the dictionary, one method would be to start at the beginning and look at each word in turn. A second method would be to start at the end and search backwards. Here, an advantage of the first method is that it would find a word faster if it were at the beginning, while the second method would be faster if the word were towards the end.

Another method for searching for the word would be one which used the fact that the words in a dictionary are in alphabetical order—this is the method we all use when looking up a word in a dictionary. In any situation, a programmer would usually have a choice of algorithms, and it is one of her more important jobs to decide which algorithm is the best, and why this is so.

In our example, we must write the instructions in our algorithm in such a way that they can be easily converted into a form which the computer can follow. Computer instructions fall into three main categories:

(1) Input instructions, used for supplying data from the ‘outside world’ to a program; this is usually done via the keyboard or a file.

(2) Processing instructions, used for manipulating data inside the computer. These instructions allow us to add, subtract, multiply and divide; they also allow us to compare two values, and act according to the result of the comparison. Also, we can move data from one location in the computer’s memory to another location.

(3) Output instructions, used for getting information out of the computer to the outside world.

Conventions (Rules) for creating Variable

2010-12-12T01:49:00.000-08:00

1. First Character of variable should be an alphabet

2. The name of variables can be in lower case as well as upper case.

3. Two or more variables cannot have same name.

4. It Cannot contain any space in between variable name.

5. It cannot contain Period Sign ( . )

6. We cannot use keywords as variable names i.e. variable name like int, float, if are invalid.

7. No special symbol is allowed in variable name.

8. A variable name should not be more than 40 characters, but it is safer to declare variable name as short as possible

Example

int a,b,c;

int a=10, b=20, c;

Definition of Variables

2010-12-12T01:41:00.000-08:00

Variable is a quantity, which my vary during program execution. Basically variable are name given to the location in the memory of computer, where different constants are stored. If a program works on some variables then we need to declare these variables with the help of data types

Histoy of C Language

2010-12-06T11:14:00.000-08:00

Histoy of C Language

The development of Unix in the C language made it uniquely portable and improvable.

The first version of Unix was written in the low-level PDP-7 assembler language. Soon after, a language called TMG was created for the PDP-7 by R. M. McClure. Using TMG to develop a FORTRAN compiler, Ken Thompson instead ended up developing a compiler for a new high-level language he called B, based on the earlier BCPL language developed by Martin Richard. Where it might take several pages of detailed PDP-7 assembly code to accomplish a given task, the same functionality could typically be expressed in a higher level language like B in just a few lines. B was thereafter used for further development of the Unix system, which made the work much faster and more convenient.

When the PDP-11 computer arrived at Bell Labs, Dennis Ritchie built on B to create a new language called C which inherited Thompson's taste for concise syntax, and had a powerful mix of high-level functionality and the detailed features required to program an operating system. Most of the components of Unix were eventually rewritten in C, culminating with the kernel itself in 1973. Because of its convenience and power, C went on to become the most popular programming language in the world over the next quarter century.

Definition of Algorithms OR What are Algorithms

2010-12-02T09:01:00.003-08:00

Definition of Algorithms OR What are Algorithms

Algorithms are used to solve a problem step by step using english language. It is the part of software designing. An algorithm defines as the step by step procedure or method that can be carried out for solvingprogramming problems. An algorithm tells computer that how to solve problem systematically to get desired output. Mainly we follow following steps to design an algorithm.

Step 1 - START

It represents beginning of the algorithm.

Step 2 - DECLARE

The variables used in algorithm are declared in this step.

Step 3 - INPUT

Here we input the values

Step 4 - FORMULA

The required result is generated in this step.

Step 5 - OUTPUT

It displays the output or result.

Step 6 - STOP

It is an end of Algorithm

Advantages of C

2010-12-02T09:01:00.001-08:00

C is Portable

This means a program written for one computer may run successfully on other computer also.

C is fast

This means that the executable program obtained after compiling and linking runs very fast.

C is compact

The statements in C Language are generally short but very powerful.

Simple / Easy

The C Language has both the simplicity of High Level Language and speed ofLow Level Language. So it is also known as Middle Level Language

C has only 32 Keywords

C Compiler is easily available

C has ability to extend itself. Users can add their own functions to the C Library

Introduction to C Language

2010-12-02T08:58:00.000-08:00

The C Language is one of the most powerful language. In the beginning due to the different architectures available, the programmer had to learn different languages to create different types of applications. To overcome this problem in 1972, Dennis Ritche at theAT & T Bell Laboratories, USA developed C Language.

It is a combination of BCPL and B Language. The problem with Low Level Languages is that they are very difficult for the humans to understand and developed. On the other hand, High Level Languages are easy for the humans to understand but slow in speed.

The C Language is high speed and easy to understand, so it is also term as Middle Level Language.

DECLARE ARRAYS

2007-08-28T21:36:00.005-07:00

An array must be declared with type of variable or data type
An array contains same type of data
e.g. – int a [10]
The name of array cannot be same as that of any other variable within the function.
The size of array is specified using sub-script notation (index)
THE sub-script indicates that how many elements are to be allocated to an array.
A sub-script used to declare an array is called dimension

ARRAYS

2007-08-28T21:36:00.003-07:00

Arrays are widely used data type in ‘C’ language. It is a collection of elements of similar data type. These similar elements could be of all integers, all floats or all characters. An array of character is called as string whereas and array of integer or float is simply called as an array. So array may be defined as a group of elements that share a common name and that are defined by position or index. The elements of an arrays are store in sequential order in memory.

WAP to input your name and display it

#include

void main ( )

{

char nm [15];

clrscr ( );

printf (“enter your name”);

gets (nm);

printf (“name is %s”,name);

getch ( );

}

STRING

2007-08-28T21:36:00.001-07:00

String are the combination of number of characters these are used to store any word in any variable of constant. A string is an array of character. It is internally represented in system by using ASCII value. Every single character can have its own ASCII value in the system. A character string is stored in one array of character type.

e.g. “Ram” contains ASCII value per location, when we are using strings and then these strings are always terminated by character ‘\0’. We use conversion specifier %s to set any string we can have any string as follows:-

char nm [25]

When we store any value in nm variable then it can hold only 24 character because at the end of the string one character is consumed automatically by ‘\0’.

1. strlen - string length

2. strcpy - string copy

3. strcmp - string compare

4. strups - string upper

5. strlwr - string lower

6. strcat - string concatenate

7. strstr - string string

JUMPS STATEMENTS

2007-08-28T21:34:00.004-07:00

These are also called as branching statements. These statements transfer control to another part of the program. When we want to break any loop condition or to continue any loop with skipping any values then we use these statements. There are three types of jumps statements.

1. Continue

2. Break

3. Goto

Continue

This statement is used within the body of the loop. The continue statement moves control in the beginning of the loop means to say that is used to skip any particular output.

Example:

WAP to print series from 1 to 10 and skip only 5 and 7.

#include

void main ( )

{

int a;

clrscr ( );

for (a=1; a<=10; a++)

{

if (a= =5 | | a= = 7)

continue;

printf (“%d \n”,a);

}

getch ( );

}

Break

This statement is used to terminate any sequence or sequence of statement in switch statement. This statement enforce indicate termination. In a loop when a break statement is in computer the loop is terminated and a cursor moves to the next statement or block;

Example:

WAP to print series from 1 to 10 and break on 5

#include

void main ( )

{

int a;

clrscr ( );

for (a=1; a<=10; a++)

{

if (a= =5)

break;

printf (“%d \n”,a);

}

getch ( );

}

Goto statement

It is used to alter or modify the normal sequence of program execution by transferring the control to some other parts of the program. the control may be move or transferred to any part of the program when we use goto statement we have to use a label.

WAP TO FIND IF NUMBER=10 THEN GOOD ELSE BAD

#include

void main ()

{

int a;

clrscr ();

printf ("Enter any Number: ");

scanf ("%d",&a);

if (a= =10)

goto g;

else

goto b;

printf ("Good");

goto end;

printf ("Bad");

goto end;

end:

getch ();

}

WAP TO PRINT SERIES FROM 1 TO 10

#include

void main ()

{

int a;

clrscr ();

a=1;

check:

if (a< =10)

goto inc;

else

goto end;

inc:

printf (“%d \n”,a);

goto check;

end:

getch ( );

}

NESTED LOOP

2007-08-28T21:34:00.003-07:00

These loops are the loops which contain another looping statement in a single loop. These types of loops are used to create matrix. Any loop can contain a number of loop statements in itself. If we are using loop within loop that is called nested loop. In this the outer loop is used for counting rows and the internal loop is used for counting columns

SYNTAX:-

for (initializing ; test condition ; increment / decrement)

{

statement;

for (initializing ; test condition ; increment / decrement)

{

body of inner loop;

}

statement;

}

PROGRAM

#include

void main ( )

{

int i, j;

clrscr ( );

for (j=1; j<=4; j++)

{

for (i=1; i<=5; i++)

{

printf (“*”)

}

printf (“\n”);

}

getch ( );

}

OUTPUT OF THIS PROGRAM IS

* * * *
* * * *
* * * *
* * * *

LOOPING

2007-08-28T21:34:00.001-07:00

These statements are used to control the flow of the program and repeat any process multiple times according to user’s requirement. We can have three types of looping control statements.

1. While

2. Do-while

3. For

While

It is an entry control loop statement, because it checks the condition first and then if the condition is true the statements given in while loop will be executed.

SYNTAX:-

Initialization;

while (condition)

{

Statements;

Incremental / decrement;

}

Do-while

Do-while loop is also called exit control loop. It is different from while loop because in this loop the portion of the loop is executed minimum once and then at the end of the loop the condition is being checked and if the value of any given condition is true or false the structure of the loop is executed and the condition is checked after the completion of true body part of the loop.

SYNTAX:-

Initialization

{

Statement;

Increment / decrement;

}

while (condition)

For loop

It is another looping statement or construct used to repeat any process according to user requirement but it is different from while and do-while loop because in this loop all the three steps of constructions of a loop are contained in single statement. It is also an entry control loop. We can have three syntaxes to create for loop:-

for (initialization;

Test condition; Increment / decrement)

{

Statement;

}

for (; test condition; increment / decrement)

{

Statement;

}

for (; test condition;)

{

Statement;

Increment / decrement

}

#include

void main ( )

int a;

clrscr ( );

for (a=1; a<=10; a++)

{

printf (“%d \n”,a);

}

getch ( );

}

SWITCH CASE / SELECT CASE

2007-08-28T21:33:00.002-07:00

These statements are used with the replacement of if-else and these statements are used when we have multiple options or choices. These choices can be limited and when we use switch case we can use only integer or character variable as expression.

#include <stdio.h>

void main()

{

int,ch qty;

long tb,dis,nb;

clrscr();

printf("1.BPL\n2.Onida\n3.Sony\n4.Samsung\n5.LG\n");

printf("\nEnter Your Choice: ");

fflush(stdin);

scanf("%d",&ch);

printf("Enter Qty: ");

scanf("%d",&qty);

switch(ch)

{

case 1:tb=(long)qty*10000;

printf("\nBPL is %ld",tb);

break;

case 2:tb=(long)qty*12000;

printf("\nOnida is %ld",tb);

break;

case 3:tb=(long)qty*11500;

printf("\nSony is %ld ",tb);

break;

case 4:tb=(long)qty*11000;

printf("\nSamsung is %ld ",tb);

break;

case 5:tb=(long)qty*13000;

printf("\nLG is %ld ",tb);

break;

default:

printf("Wrong Choice...");

}

dis=(tb*10)/100;

nb=tb-dis;

printf("\nDiscount is %ld",dis);

printf("\nNet bill is %ld",nb);

getch();

}

NESTED IF

2007-08-28T21:33:00.001-07:00

If within if is called nested if and it is used when we have multiple conditions to check and when any if condition contains another if statement then that is called ‘nested if’.

If the external condition is true, then the internal if condition or condition are executed and if the condition is false then the else portion is executed of the external if statement

SYTAX

if (condition)

{

…….

}

if (condition)

{

…….

}

else if (condition)

{

…….

}

else if (condition)

{

…….

}

else

{

…….

……. }

}

else

{

…….

}

CONTROL STATEMENTS

2007-08-28T21:32:00.000-07:00

These statements are used to control the flow of program by using these statements. We can jump from one statement to another statement in C language. We can have four types of control statements:-

decision making
case control statement or switch statement
looping / iteration statement
jump / branching statement

Decision making

These statements are used when we want to take any decision according to the condition or user requirement. These statements work on a particular condition. These conditions are used by using ‘if’ statement. We can have four types of conditional statements

if
if-else
if – else if
nested if

if statement is simple decision making statement, which is used to take any decision when the condition is true.

if (statement)

{

Statement;

}

if (expression / condition)

Statement;

If-else

This statement is used to make decision in C language. If the given condition is true then the cursor will move to the true portion else it will move to the false portion.

if (condition)

{

Statement;

}

else

{

Statement;

}

If else-if

This is another control statement which is used to take any decision according to the given condition. If the condition is true then the cursor will move to the true portion and if the condition is false the cursor will move to the false or else-if portion and then checks another condition. If this condition is true then it will move and run the second true portion and if the condition is false then cursor will move the next portion of if condition which is another else-if or else portion.

if (condition)

{

Statement;

}

else if (condition)

{

Statement;

}

else if (condition)

{

Statement;

}

else

{

Statement;

}

OPERATORS

2007-08-28T21:28:00.008-07:00

Every language contains variable and data types and also support the concept of operators. C language has over forty operators, but hardly all they are used. These are divided onto nine categories:-

(1) Arithmetic

(2) Assignment

(3) Logical

(4) Relational

(5) Modulas

(6) Increment / Decrement

(7) Conditional

(8) Bit wise

(9) Special

Arithmetic Operators (+ - * /)

These are the common operators used to perform any arithmetic calculations. These are basically used on minimum two variables or constants. These operators contain +, -, *, /.

Assignment Operators

These operators are used to assign any value to the variable or constant. The main assignment operator is ‘=’.

We have some short assignment operators. Suppose a=10

Logical operators

These are used to test more than one condition or we can say conditional expression, so that you can make a decision on the basis of that condition. These operators are

Relational operators

These operators are also called comparison operators. You can use relational operators, whenever you want to compare two quantities and variables or constants and you want to take decision on the basis of that condition. Then these operators are used.

We have following types of operators:-

Modulas Operator

This operator is used to find out the reminder of any value.

R=25%10 R=5

Increment / Decrement operators

These operators are also called unary operators. These operators are used when we want to perform any action on single operand. These operators are used when we want to increase or decrease value of any variable by one.

Increment operator is ++

Decrement operator is –

We have two types of unary operators

Post fix

This operator is used to assign any value of variable to another variable according to use requirement. In this operator firstly the value of a variable is copied to another variable and then the value is increased or decreased.

a=10

a++ a=11

Pre-fix

This operator is used to assign value to any variable according to user requirement, so that the same value is copied to another variable. Firstly the value of variable is increased or decreased and then it is copied to any other variable.

a=10

++a a=11

Conditional operators

These operators are also called ternary operators. These are used to check any condition or expression and can be used to compare two conditional expressions and produce a result if the condition is true or false. Operators used for conditional operators are “?” and “:”

Syntax:-

(expression / condition)? True statement (if) : false statement (else)

Bit wise operators

C is known as assembly language because it provides us bit wise operators, which are normally associated with assembly language programming. C language has a powerful set of special operators which are capable of manipulating data at bit level. These are as follows:-

1) & - Bit wise (and)

2) ! - Bit wise (or)

3) ^ - Bit wise (exponent)

4) << - Shift left

5) >> - Shift right

Special operators

Special operators are provided by C. these operators are as follows:-

commas operators (,)
pointer operators (*, &)
sizeof ( )

Relational operators

We have following types of operators:-

Modulas Operator

This operator is used to find out the reminder of any value.

R=25%10 R=5

Increment / Decrement operators

Increment operator is ++

Decrement operator is –

We have two types of unary operators

Post fix

a=10

a++ a=11

Pre-fix

a=10

++a a=11

Conditional operators

Syntax:-

(expression / condition)? True statement (if) : false statement (else)

Bit wise operators

1) & - Bit wise (and)

2) ! - Bit wise (or)

3) ^ - Bit wise (exponent)

4) << - Shift left

5) >> - Shift right

Special operators

Special operators are provided by C. these operators are as follows:-

commas operators (,)
pointer operators (*, &)
sizeof ( )

MACRO

2007-08-28T21:28:00.007-07:00

Macro is a substitution of a string that is placed in a program. It is placed by the definition when program is compiled and we have to use (#) symbol in front of this. We can have different macros like:-

#define, #if, #else.

It is different from preprocessor directive, because pre processor directive is used to link files with the object code and macro is used to define any string and we always or maximum use #define macro.

#include <stdio.h>

#define wait getch ( )

# define flot float

void main ( )

…….

flot f,c;

…….

wait;

}

TYPE CASTING

2007-08-28T21:28:00.005-07:00

It is used to convert on data at a time. It is required to used different type of constants and variables in expression then we have convert that expression into another data type, but certain rules are used during conversion of data type the computer consider one operand at a time involving two operands. We can have two types of type casting.

1. Implicit

2. Explicit

Implicit

When we are converting any data type which contains shorter values then along data type that conversion is called implicit or in simple language we can say when user do not need to convert any data type into another data type and it is automatically done through computer system that is called implicit type conversion. The conversion is not transparent to the user or the programmer and is done by the compiler. This converts narrow type to wider type so that use can avoid the information to the system.

#include

void main ()

{

float c,f;

clrscr ();

printf ("Enter the value of celcius: ");

scanf ("%f",&c);

f=9.0/5.0*c+32;

printf ("\Fehranite is %.2f",f);

getch ();

}

Explicit

Explicit type casting is done by the programmer manually. When the programmer wants a result of an expression to be in particular type, then we use explicit type casting. This type casting is done by casting operators ‘( )’ and data type.

#include

void main ()

{

float c,f;

clrscr ();

printf ("Enter the value of celcius: ");

scanf ("%f",&c);

f=(float) 9/5*c+32;

printf ("\Fehranite is %.2f",f);

getch ();

}

HEADER FILES

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Conio.h

It is a library file which is included in the program this is used to use

Clrscr ( )

getch ( )

getchar ( ) etc.

We do not need to include this file in C program. It is necessary for C++ programs. Conio stands for CONsole Input Output header file.

Math .h

This file is used for mathematical functions. These functions are like excel functions:-

Eg. pow( ), sqrt ( ), sin ( ), tan ( ) etc.

DECLARE VARIABLE

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When we want to declare any variable, then we decide that what is a data type of the variable? And how it should declare? Variable can eight characters long only.

VARIABLES

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It is the name given to stored reason of the memory and it provides us the facility to change the value of it during the execution. Variable names are the name given to the location in memory of a computer where different values are stored. The location which contains these constants can be an integer, character, real numbers.

CONSTANTS

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A constant represents that what a value is stored in it cannot be changed anytime. We use “const” keyword for declaring any variable as constant. This keyword is a guideline to a compiler that the value of variable is not changeable at any time during the execution of the program.

CHARACTER SET

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A character contains any alphabet, digit or special symbol to represent information. The set or character which is valid in C program is called character set. The set includes some graphic characters. Graphic characters contain alphabets, digits and some special symbols. C language uses case letters (a to z), the digit (0 to 9) and certain special characters like constants, variables, operators etc. and some special symbols:- $, <, >, <=, =, !, # etc.

Non graphical character sets contain white spaces these are also called escape sequences.

DFUNDAMENTAL DATA TYPES

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Integer data type

It is a data type which is used to hold data in whole number e.g. 40, 4, 97, 80 and its range is from -32768 to 32767. When we want to use integer data type, we have to specify “int” keyword. It takes two bytes in memory and the conversion specifier is %d.

Float type

This data type is used to store fractional numbers or these numbers are also called real numbers. In simple language we can say, this data type contains decimal value upto six decimal places. When we use decimal values to store then we can use it.

e.g. 49.797, 79718.80

it can hold either positive or negative value with or without decimal the conversion specifier used for float is %f. the range of float is -3.4*10^-38 to 3.4*10³⁸. it consumes 4 bytes in memory.

Character data type

This data type is used to store character enclosed in a pair of single quotes. E.g. ‘A’, ‘B’, ‘a’or even a blank space can be used as a character. This data type contains one byte on memory and the conversion specifier is %c.

STRING

We can also store number of characters in char data type within the range of -128 to 127. so when we store number of characters in char data type then it is converted into string data type. And we use conversion specifier %s.

Double data type

This data type is also used to store real type numbers and the keyword “double’ is used. It can hold values upto 16 decimal places and it consumes 8 bytes of memory. The conversion specifier is %lf. Its range is from 1.7*10^-308 to 1.7*10³⁰⁸.

Long type

It contains whole number bigger than integer value is much bigger than integer. It consumes 4 bytes of memory and its range is from -2147483648 to 2147483647. Its conversion specifier is %l. e.g. 247894, 4774863.

Boolian

This data type is used in relational operators. It gives us result in true or false. If the output is false it returns to zero (0) and if output is true it returns to one (1). Its range is from 0 to 1 and it has not any conversion specifier.

DATA TYPES

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Data types can be represented in variety of ways in any programming language, so that we can store data in system. C language provides us the way to hold any type of data in it. It is called data type. In C language data types are classified into two categories:-

1. Fundamental data type

2. Derived data type

Fundamental Data Type

These can be represented on the particular machine and these are provided by every language because without using data types we can’t save our data and can be called as storage media.

Derived Data Type

These are those data types which are consisting of combination fundamental data types

PSEUDO CODE

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These are basically the instructions written in plain English to solve any problem. It makes a layman understand the complexity of the problem. Pseudo is a way of describing and algorithm without using any specific programming language. It can be the example of real life examples, but it cannot be implemented in computer. It is written roughly at same level of detail.

WHAT ARE KEYWORDS?

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These are the words which are used by the compiler and have a specific meaning for the compiler. “C” has 32 keywords. Programs are written in free format; means there is no need or no rule to write instruction in one line. Few keywords are:-

else, int, float, const, void etc.

FUNCTIONS

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#include (Pre-processor directive)

Pre processor directive is a directive which is executed at the starting of the program. This directive contains # symbol and include statement (#include). This include statement is used to include any file in your program. This file can be library file or user defined file. When we use #include, this statement then pre processor tells the compiler to include the content of stdio.h because this file contains all the standard input and output functions in it.

void main ( )

This function tells the compiler for the entry point of the program. Without the main function out program cannot run and the body of the function is written in these curly braces [ { } ] and these curly braces contains number of statements, functions and expressions, keyword etc. in it. Void is a data type which tells the compiler that our main function is not returning any value to any other program of functions.

printf ( )

This function is pre defined function which is defined in our header file called standard input/output file. By using this function, we can display any constant message or any variable value on the screen. Printf stands for print format.

clrscr ( )

This function is used to clear our output screen because it remains or displays the output of last executable program and this function clears our output screen before displaying any message on the screen and this function should be used in main function. Before the declaration of variables this function will not work and this function is in conio.h file.

Stdio.h

It stands for standard input output header file. This file includes all type of input/output functions. For example:-

printf ( ), scanf ( ) etc.

//wap to print addition of two constants

#include

void main ( );

{

const int a=20;

const int b=30;

int c;

clrscr ( );

c=a+b;

printf (“Sum is %d”,c);

}

COMMENTS

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Comments are non-executable code statements. These are always ignored by the compiler, when we compile our program with the help of comments we can give description about the program or any particular statement number of comments can be given in a program. We can have two types of comments.

1. Single line comments

2. Multi line comments

1. Single line comments

These comments are used when we want to display any statement or write any statement in the program for the knowledge of user. We can use single line comments by using double slash (//) symbol.

For example:-

//single line comment

2. Multi line comment

These are used when we want top write numbers of statements which should be ignored by the compiler and also displayed in the program. To display multi line comments we use slash star (/*) in front of the starting line which should be displayed as comment and star slash (*/) at the end of the statement

For example:-

/* …………………….

……………………….

…………………….*/

PROGRAM STRUCTURE

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'C' is case sensitive language. It differentiates between characters written in lower case and character written in upper case. The program you have typed is also known as source code. In a program many lines of code can be written. In a 'C' program each statement is required to end with semicolon (;). A single statement can be split over multiple lines. 'C' is procedural language and each 'C' program must have function name ‘main’. The program execution starts from this function. T he statements within a function are always enclosed within opening curly bracket and closing curly bracket.

ESCAPE SEQUENCES

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Escape sequences are also called white spaces because they are not displayed on the screen. It consists of back slash followed by a character. The character sequence is always enclosed in the control string.

SHORTCUTS

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Click here or on the picture to enlarge it

PROGRAMMING TECHNIQUES

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Programming techniques are required to make the program simple, efficient easy to read and maintain some scientific methods have been developed to design any program. We can have three types of programming techniques.

1. Top down design

2. Bottom up design

3. Modular design

1. Top down Approach

In this program technique the program is designed by breaking it into smaller blocks, which are interlinked and called whenever needed the programmer designs the program in levels and execute the same by calling any of the level.

2. Bottom up approach

In this technique program is designed by breaking it into smaller blocks but when called it begins from smaller block to the bigger till the end of the program.

3. Modular approach

In this programming program is designed in levels where a level consists of one or more modular.

INSTALLING 'C'

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1. Find turboc.exe file.

2. Copy this file and paste it on C: drive.

3. Open DOS prompt.

4. Type cd\ and then press enter.

5. C:\> Turboc.exe –d.

6. C:\> CD tc then press enter.

How to invoke in 'C'

Start è Run è Command & then press enter

C:\tc\bin >TC then press enter

WHAT IS 'C' LANGUAGE?

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'C' language is one of the most powerful language. It is a programming language, which is firstly used to develop operating system. It is the middle level language. It was developed at AT & T BELL LABORTARIES, USA by DENID RITCHI in 1972. This is general purpose language.

History of 'C' Language

Before the development of 'C' language there were many languages but these languages provide the functionality for specific purpose. For example:- for commercial applications where a lot of data is to be used, save and retrieved, then COBOL language is used, for engineering and scientific applications, which needs more calculation power of data storage and retrieval we use FORTRAN language. There was a need for a common language for all these purpose of 'C' language is being developed. It is a combination of BSPL and ‘B’ language. It was basically used for their own purpose. So 'C' language is sometimes refers to as a high level language or a high level assembly language. If you will program in assembly language, you will find that it is look like assembly language.

Advantages of 'C' language

1. 'C' is portable means to say program written in one computer may run on another computer successfully.

2. 'C' is fast. It means that the executable program obtained after compiling and linking runs very fast.

3. 'C' is compact. It means that the statements written in 'C' language are generally short, but are very powerful. Several operations can be combined together in just one statement.

4. The 'C' language has both simplicity of high level language and low level language

FLOW CHART

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Flow char is a graphical representation of algorithm. It is used to represent algorithm steps into graphical format. It also gives us an idea to organize the sequence of steps or events necessary to solve a problem with the computer. In other words flow charts are symbolic diagrams of operations and the sequence, data flow, control flow and processing logic in information processing. These charts are used to understand any working sequence of the program.

Advantages of flowchart:-

1. It provides an easy way of communication because any other person besides the programmer can understand the way they are represented.

2. It represents the data flow.

3. It provides a clear overview of the entire program and problem and solution.

4. It checks the accuracy in logic flow.

5. It documents the steps followed in an algorithm.

6. It provides the facility for coding.

7. It provides the way of modification of running program.

8. They shows all major elements and their relationship.

Click on image to enlarge it..

Terminator

This symbol represents the beginning and end point in a program. We use start and stop option in it.

Input/Output Symbol

This symbol is used to take any input or output in the algorithm.

Process Symbol

A rectangle indicates the processing, calculation and arithmetic operations

Decision Symbol

It is used when we want to take any decision in the program.

Connector Symbol

This symbol is used to connect the various portion of a flow chart. This is normally used when the flow chart is split between two pages

Data Flow Symbol

This symbol is used to display the flow of the program. It shows the path of logic flow in a program.

ALGORITHM

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When we want to write a program it is firstly required to develop a working logic of the program that is to be written. Algorithm helps us to do this. It is a sequence of instruction to carry out in order to solve a program it is step by step continuing of any working logic.

Steps:-

1. Start

2. Input

3. Processing

4. Output

5. Stop

E.g.

1. Start

2. Let a=10, b=20

3. c=a+b

4. Print c

5. Stop

Merits/Advantages of Algorithm

1. It makes the program easy to read and understand.

2. It makes the program portable and efficient.

3. It displays easy steps of processing.

4. It simplifies the modification and to update of the existing program.

5. It provides the facility for testing a program at developing stage.

TRANSLATORS

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Computer understands the instructions written in machine language. Thus the program written in any other language needs to be translated into machine language. This task is done by translators which are special program to check user program grammatically and produce a corresponding set of machine language. There are two types of translators.

(1) Compiler

(2) Interpreter

Compiler

A compiler is a special program which checks the entire use program (source code) at once and produced to complete code into machine language or object code if there are errors in the source code. It will display all the errors at once so that you can remove all the errors and execute the program. It will not convert the source code into object or executable code. If there is any error in the source code and after removing all the errors it converts t he whole program into object code.

Interpreter

It is also a translator but functioning of it is different from compiler because it translates one statement at a time. It translates and executes the first instruction before going to second error. Checking is easier in this case because of line by line translation. The only disadvantage of this translator is that it takes more time for execution.

COMPUTER LANGUAGE

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When anyone wants to communicate to any other person then a language is followed. So if we want to communicate with computer system then we have to use computer language. We can have two types of computer languages

(1) Low Level Language

(2) High Level Language

Low Level Language

Low level language is the language which is easily understood by the computer system. This language is also called machine language or 1^st generation language of the computer. Machine language is written in binary form. So every data and instruction should be given in the form of binary language.

Computer cannot understand the language spoken by human being. So instructions are converted into binary form and if the programs are written in machine code then our system can run the instruction very fast because it is directly understood by computer system but a single disadvantage of this language is that it is machine dependent.

High Level Language

The language that makes easier for the programmer to write instructions in the language. He/She commonly uses the English language, but our computer does not understand this language directly because it understands only machine language. High level language is machine independent, means to say that instructions written in high level language are automatically converted into low level language by translator and can run on different computers without any modification. The only disadvantage of this language is that it needs to be converted into machine language, which makes the program executable. This language runs slower that low level language because firstly it is converted into low level language.