用Python计算信用支付

Question

Python初学者。我必须编写一个程序，生成一个表格，显示“信用卡”类型的余额，不管用最低付款额还清余额需要多少个月。我想我已经解决了大部分问题，但我遇到了一个问题

问题是如何在余额付清后结束循环，同时使最终付款等于余额。由于最低付款额大于上一次付款的余额，因此我的最终余额为负数。我试图通过向循环中添加一个if-then语句来解决这个问题，但最终我得到了.04的付款，而示例输出中的零价格为3.80美元

到目前为止，我掌握的代码是：

listedPrice = 200

print("%10s%20s%20s%20s%10s%20s" % \
     ("Month", "Starting Balance", "Interest to Pay", "Principal to Pay", "Payment", "Ending Balance"))

downPayment = listedPrice / 10
balance = listedPrice - downPayment
interestRate = .12
interest = (balance * interestRate) / 12 
payment = (5 * balance) / 100
principal = payment - interest
numPayments = 24

for month in range(1, numPayments +1):
    balance = balance
    interest = balance / 100
    principal = payment - interest
    endBalance = balance - payment + interest
    print("%10s%20.2f%20.2f%20.2f%10.2f%20.2f" % \
        (month, balance, interest, principal, payment, endBalance))
    if endBalance < payment:
        payment = endBalance
    balance = endBalance

或者，我尝试了以下while循环：

month = 1

while balance > 0.0:
    balance = balance
    interest = balance / 100
    principal = payment - interest
    endBalance = balance - payment + interest
    print("%10s%15.2f%15.2f%15.2f%15.2f%15.2f" % \
        (month, balance, interest, principal, payment, endBalance))
    if endBalance < payment:
        payment = endBalance
        balance=endBalance
        month+=1
        break
    balance = endBalance
    month +=1

问题是表的最后一行停止了，支付了9美元，期末余额为3.80美元。它应该还有一行，付款为3.80，期末余额为0

感谢扎克·穆罕默德提出的中断命令的想法

Answer 1

我也是Python的新手，但我喜欢解决这些问题。这有助于我更好地理解语言，提高我解决问题的能力

尽管我知道这不是“最干净”或“最有效”的代码，但我仍然可以解释什么是错误的，以及我做了什么来修复它，我相信您可以从那里找到其他解决方案

这就是我如何解决你的两个问题：

listedPrice = 200

print("%10s%20s%20s%20s%10s%20s" % \
     ("Month", "Starting Balance", "Interest to Pay", "Principal to Pay", "Payment", "Ending Balance"))

downPayment = listedPrice / 10
balance = listedPrice - downPayment
interestRate = .12
interest = (balance * interestRate) / 12 
payment = (5 * balance) / 100
originalPayment = (5 * balance) / 100
principal = payment - interest
numPayments = 24

for month in range(1, numPayments +1):
    balance = balance
    interest = balance / 100
    principal = payment - interest
    endBalance = balance - payment + interest
    if payment == 9:
        print("%10s%20.2f%20.2f%20.2f%10.2f%20.2f" % \
            (month, balance, interest, principal, payment, endBalance))
        if endBalance < payment:
            payment = endBalance
        balance = endBalance
    elif payment <= originalPayment and balance != 0:
        payment = balance + interest
        principal = balance
        endBalance = 0
        print("%10s%20.2f%20.2f%20.2f%10.2f%20.2f" % \
            (month, balance, interest, principal, payment, endBalance))
        balance = endBalance
        print("\n It took",month,"months to pay off your credit card.")

从第1个月到第23个月；因为第24个月将是0美元，不应显示。然后让你知道花了多少个月

你的问题是你没有在最后一行打破循环，改变打印语句；随着计算，需要发生给你最后的最低付款线，完成循环，然后告诉你花了多少个月

注意：我添加了最后一次付款的.04利息，因此它是3.84次付款，如果出于任何原因，最后一次付款不包括利息，您只需从最后一次'elif声明'中取出即可。我注意到你在最初的问题中说你不想要它

但由于这是一张信用卡，我认为从技术上讲，最后一笔付款应该有利息，即使是四美分。但是，如果您的指示是对最后一笔付款不感兴趣，只需将其从“for statement”的最后一个循环中删除即可

那你该走了

Answer 2

我很乐意提供帮助。首先，我无法复制您自己在错误显示$3.80时遇到的问题，但您已接近成功。我在if语句后添加了一个中断，该中断将中断循环：

if endBalance < payment:
        payment = endBalance
        break