C++ 为什么会输出错误的复利？

Question

一段时间以来，我一直在努力解决这个问题，我认为这与我用于计算的值有关。我对复利不是很熟悉，所以我不确定我是不是错了。任何帮助，将不胜感激。

#include <iostream>
#include <cmath>
using namespace std;

double interest_credit_card(double initial_balance, double interest_rate, int payment_months);
// Calculates interest on a credit card account according to initial balance,
//interest rate, and number of payment months.

int main ()
{
  double initial_balance, interest_rate;
  int payment_months;
  char answer;

  do
    {

      cout << "Enter your initial balace: \n";
      cin >> initial_balance;
      cout << "For how many months will you be making payments?\n";
      cin >> payment_months;
      cout << "What is your interest rate (as a percent)?: %\n"; 
      cin >> interest_rate;
      cout << endl;

      cout << "You will be paying: $ " <<  interest_credit_card( initial_balance,  interest_rate,  payment_months) << endl;

      cout << "Would you like to try again? (Y/N)\n";
      cin >> answer;

    }while (answer == 'Y' || answer == 'y');

  cout << "Good-Bye.\n";

  return 0;
}

double interest_credit_card(double initial_balance, double interest_rate, int payment_months)
{
  double compound_interest, compounding, compounding2, compounding3, compounding4;

  while(payment_months > 0)
    {
      initial_balance  = initial_balance + (initial_balance * interest_rate/100.0);
      compounding =  (interest_rate /12);
      compounding2 = compounding + 1;
      compounding3 = interest_rate * (payment_months/12);
      compounding4 = pow(compounding2, compounding3);
      compound_interest = initial_balance * compounding4;

      initial_balance = initial_balance + compound_interest;

      payment_months--;
    }

  return initial_balance;
}  

输入和预期输出:

Enter your initial balance: 1000
For how many months will you be making payments?: 7
What is your interest rate (as a percent)?: 9
You will be paying: $1053.70

Answer 1

看起来你尝试了一堆东西然后把它们留在了里面。你尝试的第一个解决方案几乎是正确的，你只是忘记了“/12”:

double interest_credit_card(double initial_balance, double interest_rate, int payment_months)
{
    while (payment_months > 0)
    {
        initial_balance = initial_balance + (initial_balance * interest_rate / 100.0/12);

        payment_months--;
    }

    return initial_balance;
}

有一点更好的风格:

double interest_credit_card(double initial_balance, double interest_rate, int payment_months)
{
    double total_payment = initial_balance;
    double monthly_rate = interest_rate / 100.0 / 12;
    for (int month = 1; month <= payment_months; ++month)
        total_payment += total_payment * monthly_rate;

    return total_payment;
}