输出向后输入数字的Python列表

Question

I have a need for a code that asks for input of 5 pos numbers, then outputs these numbers backwards. I would like to use a while loop. This is what I've come up with so far, but it the second while loop doesn't work.

positiveNum = 0
SIZE = 5
numberList= []
ARRAY_LIMIT = SIZE -1

while len(numberList) < SIZE :
    positiveNum = input("Enter a positive number:")
    numberList.append(positiveNum)
while int(positiveNum) >= 0:
    print(numberList[positiveNum])
    positiveNum -= 1

Answer 1

You should be iterating on length of numberList and not positive num. Basically modify second while loop to this.

 i = SIZE; 
 while i>0: 
        print(numberList[i-1])
        i=i-1

Answer 2

On the second loop, you are using the same positiveNum variable without reseting it to the size of the array, try:

SIZE = 5
numberList= []
ARRAY_LIMIT = SIZE -1

while len(numberList) < SIZE :
    positiveNum = input("Enter a positive number:")
    numberList.append(positiveNum)
index = SIZE - 1
while index >= 0:
    print(numberList[index])
    index -= 1

Answer 3

Your first issue is that input returns a string so you need to cast it to an int if you want to index with it. You are likely getting the following error.

TypeError: list indices must be integers or slices, not str

# Won't work with string
numberList[positiveNum]
positiveNum -= 1
# Need to cast to int first
positiveNum = int(input("Enter a positive number:"))

Converting it in your while loop condition will only work for the condition, it does not change that value in the variable to an int , it is still a string

# Works only once
while int(positiveNum) >= 0:

Now the next issue is that you are using positiveNum as the index number. This will cause an IndexError if the last number entered is greater than SIZE , say 100.

SIZE = 5
number_lst = []

while len(number_lst) < SIZE:
    # Should perform error checking if you must have positive numbers
    num = int(input("Enter a positive number: "))
    number_lst.append(num)

# Output backwards using while
i = len(number_lst) - 1
while i >= 0:
    print(number_lst[i])
    i -= 1

Here is also a couple of for loop alternatives

# Output backwards using for
for item in number_lst[::-1]:
    print(item)

for item in reversed(number_lst):
    print(item)

for i in range(len(number_lst) - 1, -1):
    print(number_lst[i])

for i in reversed(range(len(number_lst))):
    print(number_lst[i])

Answer 4

Using while loops:

size = 5
number_list = []

while len(number_list) < size:
    number_list.append(int(input("Enter a positive number: ")))
i = 1
while i <= size:
    print(number_list[size - i])
    i += 1

Using a for loop for the second loop:

size = 5
number_list = []

while len(number_list) < size:
    number_list.append(int(input("Enter a positive number: ")))
for i in number_list[::-1]:
    print(i)

Using two for loops, which would be more sensible in this case:

size = 5
number_list = []

for _ in range(size):
    number_list.append(int(input("Enter a positive number: ")))
for i in number_list[::-1]:
    print(i)