How to find empty space in a rectangle which has 2 circles in it?

Question

I'm solving a problem in Toph . In this problem I've to find out the empty space of a rectangle which has 2 equal circles in it.

here is the problem

#include <stdio.h>
float pi=3.1416;
int main()
{
    int i,t;
    float r,rest;
    scanf("%d",&t);
    for(i=1;i<=t;i++)
    {
        scanf("%f",&r);
        rest=(4*r*2*r)-(2*pi*r*r);
        printf("Case %d: %.2f\n",i,rest);
    }
    return 0;

Here is my solve. It returns a correct value for first test case but it fails to solve the second one. What's the problem???

Answer 1

float pi=3.1416; is the cause of the problem. Under the math header file (#include <math.h>) there is a constant M_PI use it instead.

Edit: Sorry, didn't read thoroughly, apparently the problem is in the floating point precision. If you change all float values into double it should work.

#include <stdio.h>
double pi=3.1416;
int main()
{
    int i,t;
    double r,rest;
    scanf("%d",&t);
    for(i=1;i<=t;i++)
    {
        scanf("%lf",&r);
        rest=(4*r*2*r)-(2*pi*r*r);
        printf("Case %d: %.2lf\n",i,rest);
    }
    return 0;
}