2.5. A simple C program

2.5.1. General form of a C program

Preprocessor directives

int main(void)
{
    declarations
    statements
}

We will see examples of each of type of statement shortly.

2.5.2. Hello World Example

/*
 * The classic 'Hello World' first program.
*/
#include <stdio.h>

int main(void)
{
   printf("Hello, World!\n");
   return 0;
}

2.5.3. Analysis of Hello World

Comments

The /* */ pair defines a comment block.

#include <stdio.h>

Definitions and prototypes are pulled from a system header file. #include "my.h" is for user defined header files. In Unix, system header files are in /usr/include with the libraries in /usr/lib or /lib. User defined headers should be in the same directory as the source code.

int main(void)

• main() is where the program begins. It is in every program. Notice that main() is a function like other functions.

• int means that it will return an integer value to the operating system. Generally main() will either be of type int or void.

• (void) means that no arguments are passed to main().

{ }

Indicates the start and end of each function or block of code. We define a block of code as a set of statements that are to be executed sequentially as a group.

printf( );

A function to print to the screen. C was one of the first languages to use a function for printing. The argument is a formated character string. \n means to start a new line.

return 0;

Return to the OS with an int value. 0 = success, 1 = failure.