Python Forum

Hi! So for my homework assignment, we have to reverse a four digit number.

# Python Class 2402
# Lesson 2 Problem 6
# Author: KitKatKarateIlluminati (491160)

FourDigit = int(input("Please enter a four digit number: "))

First = FourDigit % 10
Second = ((FourDigit % 100) - First)/10
Third = (FourDigit - (Second * 10 + First))/100
Fourth = (FourDigit - (First + Second * 10 + Third * 100))/1000

Reverse = Fourth + Third * 10 + Second * 100 + First * 1000
print(Reverse)

Can you guys please tell me why this is wrong?

Thanks in advance!

I think that the easiest way would be to convert int to a string, reverse it, construct a new string and convert it back to int. As you actually have a string as user input then you can skip conversion. Doesn't matter how many digits:

>>> num = 12345
>>> int(''.join((reversed(str(num)))))
54321

If you want to calculate, maybe have a look at builtin divmod()

First = FourDigit % 10
Second = ((FourDigit - First) % 100) /10
Third = ((FourDigit - (Second * 10 + First)) /100)%10
Fourth = (FourDigit - (First + Second * 10 + Third * 100))/1000

Or

>>> FourDigit='1234'
>>> FourDigit[::-1]
'4321'

Interesting operators and functions you should read more about:

• % operator for rest of division
  
• // operator for integer division
  
• += operator for inline add
  
• //= operator for inline integer division
  
• math.log10 -> how many digits does a number have?
  
• The inverse of math.log10 is 10 ** value
  
• divmod, also good for days, hours, minutes, seconds, microseconds
  

  seconds = 13371232
  minutes, seconds = divmod(seconds, 60)
  hour, minutes = divmod(minutes, 60)
  days, hour = divmod(hour, 24)
  print("Days:", days, "Hours:", hour, "Minutes:", minutes, "Seconds", seconds)

• reversed() vs. subscription reverse: [::-1]
  

I removed my solution.
You should do it mathematically.

You can do this :

num1 = input("Please enter a 4-digit number : ")
num2 = num1[::-1]
print(num2)

And output :

Output:
Please enter a 4-digit number : 1234
4321