C #define

The #define preprocessor directive is used to define constant or micro substitution. It can use any basic data type.

Syntax:
#define token value  

Let's see an example of #define to define a constant.

#include <stdio.h>  
#define PI 3.14  
main() {  
   printf("%f",PI);  
}  

Output:

3.140000


Let's see an example of #define to create a macro.

#include <stdio.h>  
#define MIN(a,b) ((a)<(b)?(a):(b))  
void main() {  
   printf("Minimum between 10 and 20 is: %d\n", MIN(10,20));    
}  

Output:

Minimum between 10 and 20 is: 10