Question

为什么这段代码会造成无限循环？我认为这应该是解决此类问题的合适方法。例如，如果价格为5美元，而您支付了5.47美元，该程序将打印：

Quarters: 1
Dimes: 2
Nickels: 0
Pennies: 2

但是，发生无限循环，我不确定为什么。有人知道原因吗？

price = round(float(input("Enter the price: ")), 2)
print price
paid = round(float(input("Enter the amount paid: ")), 2)
print paid
change = round(float(paid - price), 2)
print change
quarters = 0
dimes = 0
nickels = 0
pennies = 0
while change > 0.00:
    print change
    if change >= .25:
        change = change - .25
        quarters += 1
        continue
    elif change >= .1:
        change = change - .1
        dimes += 1
        continue
    elif change >= .05:
        change = change - .05
        nickels += 1
    elif change >= .01:
        change = change - .01
        pennies += 1
print "Quarters: " + str(quarters)
print "Dimes: " + str(dimes)
print "Nickels: " + str(nickels)
print "Pennies: " + str(pennies)

Answer 1

我不建议处理循环，而是建议取消已收集的更改，并优先处理较大的硬币。

price = float(input("Enter the price: "))
paid = float(input("Enter the amount paid: "))
change = paid - price

if change < 0:
   raise ValueError('Not enough paid')

quarters = change // 0.25
dimes = (change - (0.25 * quarters)) // 0.10
nickels = (change - (0.25 * quarters) - (0.10 * dimes)) // 0.05
pennies = 100 * (change - (0.25 * quarters) - (0.10 * dimes) - (0.05 * nickels))

print("Quarters: {:.0f}".format(quarters))
print("Dimes: {:.0f}".format(dimes))
print("Nickels: {:.0f}".format(nickels))
print("Pennies: {:.0f}".format(pennies))

Answer 2

代码中存在一个小错误，该错误导致该程序仅在价格和付款金额互换时才能正常工作（例如，price = 2，paid = 1）。但这不是导致无限循环的问题。

您的代码会为例如以下参数：

价格：5.6
已付费：5.4

可以从您自己的打印输出中看到无限循环的原因：

0.009999999999999275
0.009999999999999275
0.009999999999999275
0.009999999999999275
0.009999999999999275
0.009999999999999275
0.009999999999999275
...

自change < 0.01起，if子句不适用，因此永远不会离开循环。

您如何更稳健地解决问题？

这是草图

from math import floor
change = paid - price

quarters = int(floor(change / 0.25))
change -= quarters * 0.25

dimes = int(floor(change / 0.1))
change -= dimes * 0.1

nickels = int(floor(change / 0.05))
change -= nickels * 0.05

pennies = int(floor(change / 0.01))
change -= pennies * 0.01

remaining = change

print("Quarters:", quarters)
print("Dimes:", dimes)
print("Nickels:", nickels)
print("Pennies:", pennies)

我个人也将其简化为硬币类型的循环：

increments = {"quarter":0.25, "dimes": 0.1, "nickels": 0.05, "pennies": 0.01}
change_parts = {}
for inc_name, inc in increments.items():
    amount = int(floor(change / inc))
    print(inc_name, inc, amount)
    change -= amount * inc
    change_parts[inc_name] = amount

for inc_name, amount in change_parts.items():
    print(inc_name + ":", amount)

计算已付金额的变化

2 个答案: