While循环求出乘积（乘法）？

Question

I cannot seem to figure this out. I'm supposed to write a while loop that will print the product (multiply) of the numbers between 1 and 50. Here is my code:

def main():
    x = 1
    total = 0
    while x <= 50:
       total = total * x
       x*=1
  print(total)

main ()

However, Python isn't printing anything. Can anyone tell me what I'm doing wrong?

Answer 1

x = 1
while x <= 50:
   x*=1

These statements are resulting in an infinite loop since multiplying x by one will never change it. Mathematically, x * 1 -> x .

In addition, if you're trying to multiply the numbers one through fifty, you don't want this:

total = 0
for some condition:
    total = total * something

since total will forever remain at zero. Mathematically, x * 0 -> 0 .

The correct pseudo-code (which looks remarkably like Python) for getting the product of the numbers one through fifty is:

product = 1
for number = 1 through 50 inclusive:
    product = product * number

Changing your code to match that requires two things:

• total should start at one.
• you should add one to x in the loop rather than multiplying.

Answer 2

x * = 1导致无限循环

Answer 3

Your problem is that you have a while loop that never exits:

>>> import time
>>> x = 5
>>> while x < 10:
...     x*=1
...     print x
...     time.sleep(1)
... 
5
5
5
5
5
5
...

Your x*=1 is multiplying the x value by 1, effectively doing nothing. Therefore, you are calling your while loop until x is 50, but x never changes. Instead, you might want to put x+=1 , which will add 1 to x .

In your code, you also want to change the total = 0 , because we are not adding, we're multiplying. If total is 0, we are effectively calling 0*1*2*3*4... , and since anything times 0 is 0, this is rendered useless. Therefore, we set total to 1 :

def main():
    x = 1
    total = 1 #Start off at 1 so that we don't do 0*1*2*3*4...
    while x <= 50:
       total = total * x
       x+=1
    print(total)

main()

This runs as:

>>> def main():
...     x = 1
...     total = 1 #Start off at 1 so that we don't do 0*1*2*3*4...
...     while x <= 50:
...        total = total * x
...        x+=1
...     print(total)
... 
>>> main()