Hello, I used Class to find the Volume of a sphere by using the rule: volumeSphere=3/4*π*r³ but i dont know why the output is 0

Question

here i set r=4 & pi=3.14 please could someone tell me why the output is 0 ??!

#include <iostream>
using namespace std;
class vol{
private:
int r;
float pi;
int volume;

public:
void initialize();
void calc();
void showdata();
};

void vol::initialize(){
r=4;
pi=3.14;
}

void vol::calc(){
volume=(3/4)*pi*r*r*r;

}
void vol::showdata(){
cout<<"volume of sphere is: "<<volume;
}

int main() {

vol v;
v.initialize();
v.calc();
v.showdata();

return 0;
}

Answer 1

First of all, the voume of a sphere is (4πr³)/3. Secondly, you may get an incorrect answer as the result if division of two ints is an int by default, and numbers between (0,1) are rounded off to 0 for saving in an integer. Thus the result became 0. So you need to cast the return type to double or use type promotion.

Eg = Type Promotion :

4.0/3*3.14*r*r*r;
// Here the compiler automatically
// returns a float for you.

Eg = Type Casting :

float(4/3)*3.14*r*r*r; //or
static_cast<float>(4/3)*3.14*r*r*r;
// Here the compiler is forced
// to return a float even when the
// expected return value is int.

Answer 2

@Kinshuk thank u bro