Python：虽然循环/控制语句没有达到预期的结果，我该如何解决这个问题？

Question

cost = int(input("Enter the cost:\n"))
payment = int(input("Deposit a coin or note:\n"))

if payment >= cost:
    change = payment - cost
    print (change)

elif payment < cost:
    while payment < cost:
        payment = int(input("Deposit a coin or note:\n"))
        change = cost - payment
        print (change)
        break

我基本上想要“改变”的价值。

以上是错误的，因为它没有“存储”第一笔付款的价值，如果它低于成本，意识到我的错误。

cost = int(input("Enter the cost:\n"))
payment = 0
while payment < cost:
    firstpayment = int(input("Deposit a coin or note:\n"))
    payment = payment + firstpayment
    if payment > cost:
        change = payment - cost
        print ("Your change is: $",change)

Answer 1

循环条件说：

while payment< cost:

因此，当付款超过成本时，循环自动存在。因此，更简单的方法是，

while payment<cost:
    #do something
change = payment-cost

因为，当循环结束时，我们知道付款应该是＆gt; =费用......