PROGRAM STRUCTURE

Before we study the basic building blocks of the C programming language, let us look at a bare minimum C program structure so that we can take it as a reference in the upcoming chapters.

Hello World Example

A C program basically consists of the following parts:

Let us look at a simple code that would print the words "Hello World": 

#include <stdio.h> 
 
int main() 
{ 
   /* my first program in C */ 
   printf("Hello, World! \n"); 
    
   return 0; 
}

Let us take a look at the various parts of the above program:

  1. The first line of the program #include <stdio.h> is a preprocessor command, which tells a C compiler to include stdio.h file before going to actual compilation.
  2. The next line int main() is the main function where the program execution begins.
  3. The next line /*...*/ will be ignored by the compiler and it has been put to add additional comments in the program. So such lines are called comments in the program.
  4. The next line printf(...) is another function available in C which causes the message "Hello, World!" to be displayed on the screen.
  5. The next line return 0; terminates the main() function and returns the value 0.

Compile and Execute C Program

Let us see how to save the source code in a file, and how to compile and run it. Following are the simple steps:

  1. Open a text editor and add the above-mentioned code.
  2. Save the file as hello.c
  3. Open a command prompt and go to the directory where you have saved the file.
  4. Type gcc hello.c and press enter to compile your code.
  5. If there are no errors in your code, the command prompt will take you to the next line and would generate a.out executable file.
  6. Now, type a.out to execute your program.
  7. You will see the output "Hello World" printed on the screen. 
$ gcc hello.c 
$ ./a.out 
Hello, World!

Make sure the gcc compiler is in your path and that you are running it in the directory containing the source file hello.c.