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What is file inclusion in C / preprocessor directives / Micros in c

What is file inclusion in C / preprocessor directives / Micros in c:-

 Preprocessor  Directives :-   Preprocessor directives are commands to the compiler  to perform certain task  before the process of  compilation start . These  command are start form symbol ( # ) following  are main preprocessor directives. What is file inclusion in C / preprocessor directives / Micros in c

#include<stdio.h> // To include built in header files.
#include "my header .h" // to include user define header files.

 

File inclusion : –  The preprocessor  directives is used to include the  contains of predefine system header files or user header files .

Example :-        

 

Defining macros : –  Macros are basically symbolic names corresponding to some content or expression 

function before the compilation start the value corresponding to this macros is substituted in the program .

Example 1 :-

# define PI 3.14 
 int main()
 {
     float r , a ;
     scanf(" %f " , &r);
     a = PI*r*r;
     printf("Area = %f " , a);
     return 0;
 
  }

 

output:-
Area = 12.560000

 

Exampple 2:-

#define square(x)   ((x)*(x))
int main()
{
    int z = 5 , y;
    y = square(z);
    printf("square of %d is %d",z, y);
    return 0;
}

 

Output:-
square of 5 is 25
 

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