Interesting!

// A practice program to calculate a (theoretical) loan payment scheme
#include <iostream>
#include <cmath>
using namespace std;

int main ()
{
    double Principal, IntRate, PayPerYear, NumYears, Payment, numer, denom, b , e, TotalInterest = 0.0;
    double runningtotal, monthcount;

    cout << "What is the principal?\n";
    cin >> Principal;

    cout << "What is the interest rate?\n";
    cin >> IntRate;

    cout << "How many payments per year?\n";
    cin >> PayPerYear;

    cout << "How many years of payment?\n";
    cin >> NumYears;

    numer = IntRate*(Principal/PayPerYear);

    e = -(PayPerYear * NumYears);
    b = (IntRate/PayPerYear)+1;

    denom = 1 - pow(b, e);

    Payment = numer / denom;

    cout << "Payment is " << Payment;
    runningtotal = Principal;

    for(monthcount = (NumYears*12); monthcount >= 0; --monthcount) {

        TotalInterest += (IntRate * runningtotal);
        cout << "\n" << TotalInterest;
        runningtotal -= Payment;
        }

 cout << "\nPayment is " << Payment << "\n Total interest payed is " << TotalInterest << "\n";

    system("pause");
    return 0;
}