Add Comments in C

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

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

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

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.