C define directive

C define directive

Also called preprocessor directive which is used to replace the token with or without parameters with custom name.

define directive is used to define macro, macro is a fragment of code that is given a name.

We can use that fragment of code in program by using the macro name

Replaces fragment of code for defined macro before programs compilation.

define function syntax,

#define  

C program to define macros for predefined function

This c program is used to define new custom name for printf function to print the string.

#include<stdio.h>                                                               
                                                                                
#define cpf printf                                                              
                                                                                
void main()                                                                     
{                                                                               
 cpf("defines macro");                                                          
} 

Output:

$cc defines.c
$ ./a.out 
defines macro

C program to define macros for char keyword

This c program is used to deine new custom name for char keyword and used custom name to define the character array to read and print the string.

#include<stdio.h>                                                              
                                                                                
#define ch char                                                                 
#define cpf printf                                                              
                                                                                
void main()                                                                     
{                                                                               
 ch name[50] = "codingpointer.com";                                             
 cpf("welcome to %s",name);                                                     
} 

Output:

$ cc define.c
$ ./a.out 
welcome to codingpointer.com

C program to define macros for constant value

This c program is used to deine new custom name for constant value 3.14 and used custom name to compute area of circle and prints the area.

#include<stdio.h>                                                                
                                                                                
#define PI 3.14                                                                 
                                                                                
void main()                                                                     
{                                                                               
  int area, radius=10;                                                          
  area = PI*radius*radius;                                                      
  printf("\nArea of circle: %d", area);                                         
}  

Output:

$ cc define.c
$ ./a.out 

Area of circle: 314

C program to define macros for expression

This c program is used to deine new custom name for expression 3.14*radius*radius and used custom name to compute area of circle and prints the area.

#include<stdio.h>                                                               
                                                                                
#define AREA 3.14*radius*radius                                                 
                                                                                
void main()                                                                     
{                                                                               
  int area, radius=10;                                                          
  area = AREA;                                                                  
  printf("\nArea of circle: %d", area);                                         
}   

Output:

$ cc define.c
$ ./a.out 

Area of circle: 314

C program to define macros for function

This c program is used to deine new custom name for function compute_area which computes area of circle using formula (3.14*radius*radius) and used custom name to compute area of circle and prints the area.

#include<stdio.h>                                                              
                                                                                
#define AREA compute_area(radius)                                               
                                                                                
int compute_area(int radius)                                                    
{                                                                               
 return 3.14*radius*radius;                                                     
}                                                                               
void main()                                                                     
{                                                                               
  int area, radius=10;                                                          
  area = AREA;                                                                  
  printf("\nArea of circle: %d", area);                                         
}  

Output:

$ cc define.c
$ ./a.out 

Area of circle: 314