Area of Circle using function

for formula: http://www.mathsisfun.com/area.htm

code:

#include<stdio.h>
double pi=3.1416;
double britto(double r)
{
    double area=pi*r*r;
    return area;
 
}
int main()
{
double r=3;
double khetrofol=britto(r);
printf("%lf",khetrofol);
 
    return 0;
}

We have to always remember that value that define is always pass from main function to customized function named by user so here r=3 is passing to function britto and then the britto formula pi*r*r is applying and returned the value and it is printed in the main function where the variable defined as khetrofol.

Here pi declared as global variable with it’s value.