C Program Structure

Every c program contains number of several building blocks known as function. each function of it perform task independently. A function is subroutine that may consist of one or more statements.

Every full C program begins inside a function called "main".

Every program written in c language must contain main()function. The main() function is a starting point of every 'c' program. The execution of a program always begins with the main() function.

A function is simply a collection of commands that do "something". The main() function is always called when the program first executes.

The program execution starts from the opening braces { and ends with closing braces }.

#include <stdio.h>
int main()
{
    printf( "I am alive!  Beware.\n" );
    getchar();
    return 0;
}

The #include is a "preprocessor" directive that tells the compiler to put code from the header called stdio.h into our program before actually creating the executable. By including header files, you can gain access to many different functions--both the printf and getchar functions are included in stdio.h.

The next important line is int main(). This line tells the compiler that there is a function named main, and that the function returns an integer, hence int. The "curly braces" ({ and }) signal the beginning and end of functions and other code blocks.

The printf function is the standard C way of displaying output on the screen. The quotes tell the compiler that you want to output the literal string as-is (almost). The '\n' sequence is actually treated as a single character that stands for a newline.

The actual effect of '\n' is to move the cursor on your screen to the next line. Notice the semicolon: it tells the compiler that you're at the end of a command, such as a function call. You will see that the semicolon is used to end many lines in C.

Finally, at the end of the program, we return a value from main to the operating system by using the return statement. This return value is important as it can be used to tell the operating system whether our program succeeded or not. A return value of 0 means success.

return 0; terminates the main() function and returns the value 0.