#define _USE_MATH_DEFINES

#include <iostream>
#include <cmath>

using namespace std;

double sphere_volume( double radius ) {
    return M_PI * 4 / 3 * std::pow( radius, 3 );
}

int main() {
    cout << "Welcome User" << endl;

    for( ;;) {
        char option;
        cout << "Do you have diameter or ratio? (d/r/q-exit): ";
        cin >> option;

        if( 'r' == option ) {
            cout << "What is the radius?: ";
            double radius;
            cin >> radius;
            cout << "The volume is: " << sphere_volume( radius ) << endl;
        
        } else if( 'd' == option ) {
            cout << "What is the diameter?: ";
            double diameter;
            cin >> diameter;
            cout << "The volume is: " << sphere_volume( diameter / 2 ) << endl;
        
        } else if( 'q' == option ) {
            break;
        }
    }
}