We have two cases where we use file inclusion: a. If programer is dealing with a very large program. b. If similar functions and macro definitions are using frequently.

L8Q2_File_Inclusion_C_Preprocessor.c

#include<stdio.h>
#include "circle.c"
#include "circle.h"
int main()
{
    float r = 4.0;
    printf("%.2f", circle_area(r, PI));
    return 0;
}

L8Q2_File_Inclusion_Circle.c

double circle_area(float r, float PI)
{
    return (PI * r * r);
}

L8Q2_File_Inclusion_Circle.h

#define PI 3.14159265358979323846

double circle_area(float, float);