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Python program to reverse a given number (2 different ways)

Reversing a number in Python: Here, we are going to learn different ways to reverse a given number in Python.
Submitted by Ankit Rai, on July 28, 2019

Take input number from the user and print its reverse.

Example:

    Input:
    12345

    Output:
    54321

Here, we are implementing program to reversing a given number using 2 different ways.

1) Famous approach for reversing the number: Take input from the user and typecast into an integer, then iterate in the loop till num is not become zero, inside the loop:

  • Find out the remainder.
  • Using this: rev_num = rev_num * 10 + remainder.
  • Update that number by diving by 10.
  • After coming out of the loop printing the reverse number.
if __name__ == "__main__" :

    # take string input from user
    num = int(input('Enter a number: '))

    rev_num = 0

    # iterate the loop till num is not equal to zero
    while(num) :
        rem = num % 10
        rev_num = rev_num* 10 + rem
        num //= 10
    
    print('Reverse number is: ', rev_num)

Output

Enter a number: 12345
Reverse number is:  54321

2) Make a user-defined function for reversing the Number: Take input from the user and typecast into integer, thenreverseNum() function call.

Inside the function:

  • Iterate in the loop till num does not become zero:
  • Find out the remainder.
  • Using this: rev_num = rev_num * 10 + remainder.
  • Update that number by diving by 10.
  • After coming out of the loop returning the reverse number to the main.
# define a function for finding 
# reverse of the number
def reverseNum(num) :
    
    rev_num = 0

    # iterate the loop till num is not equal to zero
    while(num) :
        rem = num % 10
        rev_num = rev_num* 10 + rem
        num //= 10

    return rev_num


# Main() method
if __name__ == "__main__" :

    # take string input from user
    num = int(input('Enter a number: '))
    
    print('Reverse number is: ', reverseNum(num))

Output

Enter a number: 12345
Reverse number is:  54321





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