Question

我有一个用python 3编写的真正的基本计算器程序。第一次是这样，在给出答案后，可以提示用户做另一个问题。后续循环用于验证用户输入。

出于某种原因，内部循环工作正常，如果我选择关闭程序，主循环将工作，但是，如果我选择做另一个问题，它循环要求数字而不是开始询问什么问题。< / p>

while True:
# User inputs type of problem & input is validated
    while True:
        problem = input()

        if problem not in ('1', '2', '3', '4'):
            print('You did not make a valid selection, please try again.')
        else:
            break

# User inputs numbers for problems & input is validated
    while True:
        num1 = input('Please input the first number in the problem')
        num2 = input('Please input the second number in the problem')
        isnum1 = is_number(num1)
        isnum2 = is_number(num2)

        if isnum1 is False or isnum2 is False:
            print('You did not enter a number')
        else:
            num1 = float(num1)
            num2 = float(num2)
            break

# Perform appropriate math
    ans = 0
    if problem == '1':
        ans = num1 + num2
        print(num1, '+', num2, '=', ans)
    elif problem == '2':
        ans = num1 - num2
        print(num1, '-', num2, '=', ans)
    elif problem == '3':
        ans = num1 * num2
        print(num1, '*', num2, '=', ans)
    elif problem == '4':
        ans = num1 / num2
        print(num1, '/', num2, '=', ans)

# Ask if user would like to perform another problem or exit
    nxt = input('Would you like to do another problem?\n 1 - Yes\n 2 - No')

    if nxt not in ('1', '2'):
        print('You did not make a valid selection.')
    elif nxt == '2':
        break

exit(0)

Answer 1

你的问题是problem没有留下范围，所以仍然定义了你，并且你突破了第一个循环。

这是你的第一个循环：

while True:
    problem = input()

    if problem not in ('1', '2', '3', '4'):
        print('You did not make a valid selection, please try again.')
    else:
        break

在此之前未定义

problem。但是在此之后定义了。因此，当外部while循环循环时，问题将保持定义。因此，您的第二个if子句（else）将执行，中断。

要证明这一点，请执行以下操作：

while True:
    problem = input()

    if problem not in ('1', '2', '3', '4'):
        print('You did not make a valid selection, please try again.')
    else:
        print('You have made a valid selection: {}".format(problem))  # This will display, showing that the loop is executed.
        break

要解决此问题，请执行以下操作：

problem = None
while True:
    problem = input()

    if problem not in ('1', '2', '3', '4'):
        print('You did not make a valid selection, please try again.')
    else:
        print('You have made a valid selection: {}".format(problem))
        break

Answer 2

纳撒尼尔说，我离开了problem。但是，如果我只是在循环之前设置problem = None，则没有提示用户选择问题的说明。

所以我改变了这段代码：

    if nxt not in ('1', '2'):
        print('You did not make a valid selection.')
    elif nxt == '2':
        break

对此：

if nxt not in ('1', '2'):
    print('You did not make a valid selection.')
elif nxt =='1':
    print('Please select the type of problem you would like to complete.\n 1 - Addition\n 2 - Subtraction\n 3 - Multiplication\n 4 - Division\n')
    problem = 0
elif nxt == '2':
    break

现在一切都很好。感谢Nathaniel正确方向的观点。

while循环w / 2循环内部循环到错误的位置Python3

2 个答案: