menghiitung diameter lingkaran

#include <iostream>
using namespace std;
void dmeter(float phi, float d, float k){
        float d = k/phi;
    }
int main()
{
    const float phi = 3.14;
    float diameter, keliling;
    cout<<"berapa nilai keliling = ";
    cin>>keliling <<endl;
    cout<<"maka diameter nya adalah = ";
    cout<<dmeter(phi, diameter, keliling);
}