Check For Number Palindrome

Program Logic

• A palindrome number is the one which is same as the number when the digits in number are reversed.
• We keep a copy of original number.
• Try to create reverse number as follows :
  1. Let us say number is 121. Reverse number is initially 0.
  2. We take the last digit i.e. 1.
     Iteration 1 - last digit = 1
     Iteration 2 - last digit = 2
     Iteration 3 - last digit = 1
  3. Multiply reverse number by 10 shifting current digits to right.
     Iteration 1 - reverse number = 0*10 = 0
     Iteration 2 - reverse number = 1*10 = 10
     Iteration 3 - reverse number = 12*10 = 120
  4. Now add last digit to reverse number.
     Iteration 1 - reverse number = 0 + 1 = 1
     Iteration 2 - reverse number = 10 + 2 = 12
     Iteration 3 - reverse number = 120 + 1
  5. Remove the last digit from original number
     Iteration 1 - Original number 12
     Iteration 2 - Original number 1
     Iteration 3 - Original number 0
  5. Repeat steps 2-4 until original number becomes 0.
• Now check if reverse number and copy of original number are the same. If yes, we have a palindrome number :D

/*

 * C Program to check if a number is palindrome or not.

 */

// Includes

#include <stdio.h>

// Declarations

/* isPalindrome

 * Description : A function to check if given number is palindrome or not.

 * Parameters  : i_number - number which needs to be checked for palindrome.

 * Returns     : unsigned short 0 - if a number is not palindrome.

 *                              1 - if a number is palindrome.

 */

unsigned short isPalindrome(int i_number);

// Definitions

int main()

{

    int i_number;

    printf("Enter numbwe that needs to be checked for palindrome : ");

    scanf("%d",&i_number);

    

    // Check for palindrome.

    if (isPalindrome(i_number))

    {

        printf("Entered number %d is palindrome.\n",i_number);

    }

    else

    {

        printf("Entered number %d is not palindrome.\n",i_number);

    }

}

unsigned short isPalindrome(int i_number)

{

    int i_reverseNumber = 0;     // to store reverse number.

    int i_copyNumber = i_number; // to store number copy for modification.

    int i_lastDigit;

    

    while (i_copyNumber)         // unless number becomes 0

    {

        // Take the last digit.

        i_lastDigit = i_copyNumber %10;

        

        // Shift digits to right by 1 place.

        i_reverseNumber *= 10;

        

        // Add last digit on right

        i_reverseNumber += i_lastDigit;

        

        // Remove last digit from original number.

        i_copyNumber /= 10;

    }

    

    return i_reverseNumber == i_number;

}