[英]What am I doing wrong with this mortgage formula?
#include <iostream>
#include <cmath>
using namespace std;
/* FINDS AND INITIALIZES TERM */
void findTerm(int t) {
int term = t * 12;
}
/* FINDS AND INITIALIZES RATE */
void findRate(double r) {
double rate = r / 1200.0;
}
/* INITALIZES AMOUNT OF LOAN*/
void findAmount(int amount) {
int num1 = 0.0;
}
void findPayment(int amount, double rate, int term) {
int monthlyPayment = amount * rate / ( 1.0 -pow(rate + 1, -term));
cout<<"Your monthly payment is $"<<monthlyPayment<<". ";
}
这是主要功能。
int main() {
int t, a, payment;
double r;
cout<<"Enter the amount of your mortage loan: \n ";
cin>>a;
cout<<"Enter the interest rate: \n";
cin>>r;
cout<<"Enter the term of your loan: \n";
cin>>t;
findPayment(a, r, t); // calls findPayment to calculate monthly payment.
return 0;
}
我一遍又一遍地运行它,但它仍然给我错误的数量。 我的教授给我们举了一个这样的例子:贷款=200,000 美元
率=4.5%
期限:30 年
findFormula() 函数应该为抵押付款产生 1013.67 美元。 我的教授也给了我们那个代码(monthlyPayment = amount * rate / ( 1.0 – pow(rate + 1, -term));)。 我不确定我的代码有什么问题。
该公式可能没问题,但您没有返回或使用来自转换函数的任何值,因此其输入是错误的。
考虑对您的程序进行这种重构:
#include <iostream>
#include <iomanip> // for std::setprecision and std::fixed
#include <cmath>
namespace mortgage {
int months_from_years(int years) {
return years * 12;
}
double monthly_rate_from(double yearly_rate) {
return yearly_rate / 1200.0;
}
double monthly_payment(int amount, double yearly_rate, int years)
{
double rate = monthly_rate_from(yearly_rate);
int term = months_from_years(years);
return amount * rate / ( 1.0 - std::pow(rate + 1.0, -term));
}
} // end of namespace 'mortgage'
int main()
{
using std::cout;
using std::cin;
int amount;
cout << "Enter the amount of your mortage loan (dollars):\n";
cin >> amount;
double rate;
cout << "Enter the interest rate (percentage):\n";
cin >> rate;
int term_in_years;
cout << "Enter the term of your loan (years):\n";
cin >> term_in_years;
cout << "\nYour monthly payment is: $ " << std::setprecision(2) << std::fixed
<< mortgage::monthly_payment(amount, rate, term_in_years) << '\n';
}
它仍然缺乏对用户输入的任何检查,但鉴于您的示例的值,它输出:
Enter the amount of your mortage loan (dollars): 200000 Enter the interest rate (percentage): 4.5 Enter the term of your loan (years): 30 Your monthly payment is: $ 1013.37
与您的预期输出 (1013, 6 7) 略有不同可能是由于任何类型的舍入错误,甚至是编译器选择的std::pow
的不同重载(自 C++11 起,积分参数被提升为double
)。
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