我写了一个简单的atm机程序，但有些输入会导致0.01的差异。代码怎么了？（初学者）

Question

banknotes = [200,100,50,20,10,5,1,0.50,0.25,0.10,0.05,0.01]

amount = float(input("Enter an amount: "))

for i in range (0,len(banknotes)):
    if banknotes[i] <= amount:
        banknote = int(amount // banknotes[i])
        amount = amount - banknote*(banknotes[i])
        print(banknotes[i],"banknotes:",banknote)

例如，当我输入86.74时，程序的行为就像它的86.73。但不知何故，当我输入386.74或几乎任何其他数字时，它工作正常。我真的看不出问题出在哪里，我尝试在线python编译器来查看我的IDE是否有bug，同样的事情也发生了

Answer 1

正如评论所指出的，浮动比较并不总是准确的。如果使用整数乘以100（将所有内容视为美分并使用整数数学），这不再是一个问题：

banknotes = [20000,10000,5000,2000,1000,500,100,50,25,10,5,1]

# read a floating point into an int, could also just do int(float(input()) * 100)
def parse_input(input_str):
    split = input_str.strip().split(".")
    if len(split) == 2:
        return int(split[0]) * 100 + int(split[1])
    else:
        return int(split[0]) * 100

amount = parse_input(input("Enter an amount: "))

for i in range (0,len(banknotes)):
    if banknotes[i] <= amount:
        banknote = int(amount // banknotes[i])
        amount = amount - banknote*(banknotes[i])
        print("% .2f" % (banknotes[i] / 100,),"banknotes:",banknote)