one while loop to count up and down

user_14239005 0
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How do you write a program to count up and down from a users integer input, using only one while loop and no for or if statements?

I have been successful in counting up but can't seem to figure out how to count down. It needs to look like a sideways triangle also, with spaces before the number (equal to the number being printed).

this is my code so far;

n = int(input("Enter an integer: "))
i = " "
lines = 0
while lines <= n-1: 
    print(i * lines + str(lines))
    lines += 1
countdown python-3.7 while-loop python loops
2 Answers

You can solve this by making good use of negative numbers and the absolute value: abs() which will allow you to "switch directions" as the initial number passes zero:

n = int(input("Enter an integer: "))
s = " "
i = n * -1

while i <= n: 
    num = n - abs(i)

    print(s * num + str(num))
    i += 1

This will produce:

Enter an integer: 3
0
 1
  2
   3
  2
 1
0
user_38746230

Move the print line to after the while loop. Form a list of lists (or an array) in the while loop using the content from your current print statement. Then create a second statement in your single while loop to count down, which creates a second list of lists. Now you can sequentially print your two lists of lists.

user_52840540
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