Functions Basic 3

#include <iostream.h>

float sphere (float);
int main ()
{
    int a=0;
    cout <<"Enter The Radius Of The Sphere : ";
    cin >> a;
    cout <<"\n\nRadius of sphere is " << sphere(a);
    return 0;
}
float sphere (float x)
{
    x=4*3.14*(x*x);
    return x;
}