Pre-processor Directives in C

The C Pre processor or cpp is the macro pre-processor.

We can do below tasks using pre-processor directives.

1. Including header files
2. Expanding macro
3. Conditional compilation
4. Defining global constants.

Some examples of CPP directives are given below.

1.  #include<stdio.h> - This directive tells the CPP to include contents of stdio.h file into current c source file.
2.  #define PI 3.14 – This directive defines the constants.

We can also have directives that can be used for the conditional compilation.

#include <stdio.h>

#include <stdlib.h>

#define PI 3.14

int main()

{

#if (defined PI)

  printf(" PI is defined");

#endif

}

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