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Python Program to reverse the digits of a number

The following is a Python program to reverse the digits of a number.

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# Program to reverse the digits of a number literally
# Input  = 1234
# Output = 4321

num = int(input("Enter a number: "))

reverse = 0

while num > 0:
    rem = num % 10                  # extract the last digit
    reverse = reverse * 10 + rem    # append rem to the end of the reversed number
    num //= 10                      # drop the last digit

print("Reversed number: ", reverse)

Sample Run 1:

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Enter a number: 1478
Reversed number:  8741

Sample Run 2:

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Enter a number: 12799
Reversed number:  99721

Try it out:

# Program to reverse the digits of a number literally
# Input  = 1234
# Output = 4321

num = int(input("Enter a number: \n"))

reverse = 0

while num > 0:
    rem = num % 10                  # extract the last digit
    reverse = reverse * 10 + rem    # append rem to the end of the reversed number
    num //= 10                      # drop the last digit

print("Reversed number: ", reverse)

To reverse the digits of a number literally, here is the algorithm:

1. Extract the rightmost digit of the number being reversed.

   rem = num % 10
   

2. Increase the previously reversed integer by a factor of 10 (this has the effect of moving ones digit to the tens place, tens digit to the hundreds place and so on), and then add it to the recently extracted digit (this has the effect of placing the digit at the ones place) to obtain the current value of reverse.

   reverse = reverse * 10 + rem
   

   The reverse variable starts off with 0 and in each iteration it contains the partially reversed number. By the time the loop terminates, the reverse will contain the completely reversed number.

3. Drop the rightmost digit of the digit being reversed.

   num = num // 10
   

4. Repeat steps 1-3, until the number being reversed is reduced to 0.

Assuming, num = 4819, the while loop proceeds as follows:

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