在用户输入后重复 while 循环

Question

我需要创建一个程序，将 2 到 100 之间的偶数相加。我有这个部分：

def main():
    num = 2
    total = 0
    while num <= 100: 
        if num % 2 == 0:
            total = total + num
            num += 1
        else:
            num += 1
    print("Sum of even numbers between 2 and 100 is:", total)
main()

下一部分是我应该在当前的 while 循环中添加一个 while 循环，该循环要求输入 Y/N，如果输入为是，将重复该程序。 我花了很长时间尝试将以下内容放在不同的位置：

while again == "Y" or again == "y":
again = input("Would you like to run this again? (Y/N)")

但是我一直无法让它工作，或者在最好的情况下我让它打印数字的总数并询问我是否想再次运行它但是当我输入 yes 时它又回到询问我是否想运行再说一遍。

我把另一个 while 语句放在哪里？

Answer 1

def sum_evens():
    active = True
    while active:
        sum_of_evens = 0
        for even in range(2, 101, 2):
            sum_of_evens += even
        print('Sum of the evens is:', sum_of_evens)
        while True:
            prompt = input('Type "Y" to start again or "N" to quit...\n')
            if prompt.lower() == 'y':  # doesn't matter if input is caps or not
                break
            elif prompt.lower() == 'n':
                active = False
                break
            else:
                print('You must input a valid option!')
                continue

sum_evens()

Answer 2

如果要求再次运行程序的 while 循环不必在计算总和的循环内，那么以下内容应该回答您的约束：

def main():
    again = 'y'
    while again.lower() == 'y':
        num = 2
        total = 0
        while num <= 100:
            if num % 2 == 0:
                total = total + num
                num += 1
            else:
                num += 1
        print("Sum of even numbers between 2 and 100 is:", total)
        again = input("Do you want to run this program again[Y/n]?")

main()

请注意，如果您回答N （否，或其他非Y或y答案），程序将停止。 它不会永远要求。

Answer 3

检查您的求和是否有封闭形式总是好的。 这个系列类似于正整数之和，它有一个，所以没有理由迭代偶数。

def sum_even(stop):
    return (stop // 2) * (stop // 2 + 1)

print(sum_even(100)) # 2550

要将其放入 while 循环中，请在函数调用后询问用户输入，如果是'y'则中断。

while True:
    stop = int(input('Sum even up to... '))
    print(sum_even(stop))
    if input('Type Y/y to run again? ').lower() != 'y':
        break

输出

Sum even up to... 100
2550
Type Y/y to run again? y
Sum even up to... 50
650
Type Y/y to run again? n

Answer 4

您应该在开头添加 while 循环并在最后询问用户。 像这样：

num = 2
total = 0
con_1 = True
while con_1:
   while num <= 100:
       if num % 2 == 0:
           total = total + num
           num += 1
       else:
           num += 1
   print("Sum of even numbers between 2 and 100 is:", total)
   ask = str(input("Do you want to run this program again(Y/n)?:"))
   if ask == "Y" or ask == "y":
       con_1 = True
   elif ask == "N" or ask == "n":
       con_1 = False
   else:
       print("Your input is out of bounds.")
       break