#include <stdio.h>
#include <conio.h>

#define PI 3.14159
float cal(float radius);
int main()
{
    int i;
    float area, radius;

    printf("To stop program insert value of radius = 0...");
    printf("\n Radius of circle: ");
    scanf("%f", &radius);

    for (i = 0; radius != 0; i++)
    {
        if (radius < 0)
        {
            area = 0;
        }
        else
        {
            area = cal(radius);
        }
        printf("Area of Circle is %f \n", area);
        scanf("%f", &radius);
    }
}

float cal(float r)
{
    float a;
    a = PI * r * r;
    return (a);
}