Problem with M_PI

[bonecrunch]

Hello
I need some help with this code.

I got this expression: M = 4/3(p*pi*r^3) where p is a constant.
pi is also a constant, and to define it I used M_PI.

#include <iostream>
#include <cmath>

using namespace std;
int main(){
    double p, r;

    cout<<"Insert p value(Kg/m^3): ";
    cin>>p;
    cout<<"Insert r value(Kg): ";
    cin>>r;
    double mass=(4/3)*p*M_PI*pow(r,3);
    cout<<"The mass of the esphere is "<<mass<<"Kg"<<endl;
    return 0;
}

if I set p and r as 1, it returns 3.14..., it doesn't consider the (4/3)

Can somebody help me?

[helios]

4 is an integer and 3 is an integer, so that / means integer division. Only one 3 fits in 4, so 4/3 is 1.
If you want the fractional value do (4.0/3.0).

[bonecrunch]

oh! thanks helios !