C - 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 −

• Preprocessor Commands
• Functions
• Variables
• Statements & Expressions
• Comments

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");

return0;

}

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

· 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.

· The next line int main() is the main function where the program execution begins.

· 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.

· The next line printf(...) is another function available in C which causes the message "Hello, World!" to be displayed on the screen.

· 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 −

· Open a text editor and add the above-mentioned code.

· Save the file as hello.c

· Open a command prompt and go to the directory where you have saved the file.

· Type gcc hello.c and press enter to compile your code.

· 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.

· Now, type a.out to execute your program.

· 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.