TypeError：不支持的操作数类型为 - ：'str'和'str'？

Question

我是新来的编程和无法弄清楚如何解决这个错误：

Traceback (most recent call last): 
    File "/Users/aubreyoleary/Documents/Cashier.py", line 31, in <module> 
    changePennies = int((amountReceived - amountDue) * 100) 
TypeError: unsupported operand type(s) for -: 'str' and 'str' 

我的代码：

import math 

class Cashier: 

    def getDollars(self, x): 
     return x/100 

    def getQuarters(self, x): 
     y = x % 100 
     return y/25 

    def getDimes(self, x): 
     y = x % 100 
     return y % 10 

    def getNickels(self, x): 
     y = x % 100 
     return y % 5 

    def getPennies(self, x): 
     y = x * 1 
     return y 

while True: 

    thecashier = Cashier() 

    amountDue = input("Please enter amount due: ") 
    amountReceived = input("Please enter amount received: ") 

    changePennies = int((amountReceived - amountDue) * 100) 

    print(thecashier.getPennies(changePennies)) 
    print(thecashier.getDollars(changePennies)) 
    print(thecashier.getQuarters(changePennies)) 
    print(thecashier.getDimes(changePennies)) 
    print(thecashier.getNickels(changePennies)) 

    choice = input("Do you want to continue <yes> <no>? ") 
    if (choice == "no"): 
     print("Have a nice day. ") 
     break 

Answer 1

这意味着“6” - “4”是行不通的因为它们都是字符串。首先，您需要将字符串值转换为数字：

changePennies = int(round((float(amountReceived) - float(amountDue)) * 100, 0)) 

Answer 2

正是因为amountReceived和amountDue数据类型为字符串。在执行操作-之前，您必须将其转换为float。

代替int((amountReceived - amountDue) * 100)，使用：

changePennies = int(float(amountReceived) - float(amountDue)) * 100