This program checks whether a given integer is a palindrome.

check-palindrome-v0.c

/*
 ============================================================================
  Program Name   : Palindrome Number Checker
  Filename       : check-palindrome-v0.c
  Description    : This program checks whether a given integer is a palindrome.
                   A palindrome number reads the same forwards and backwards.
                   Example: 121, 1331, 7.

  Approach       : The number is reversed using arithmetic operations
                   (modulus and division). The reversed value is then
                   compared with the original number.

  Input          : An integer entered by the user.
  Output         : Displays whether the input number is a palindrome or not.

  Constraints    : - Negative numbers are not considered palindromes.
                   - Works for all non-negative integers within int range.

  Time Complexity: O(d), where d is the number of digits.
  Space Complexity: O(1)

  Author         : Napoleon Arouldas S.
  
  Website        : https://neps.in
  LinkedIn       : https://www.linkedin.com/in/meetneps
  
  Created On     : 12-06-2000
 ============================================================================
*/


#include <stdio.h>

// Adding constants for easy readability.
#define TRUE 1
#define FALSE 0

int isPalindrome(int n){
	int i,r,rev,n_preserved,palindrome;

	// initialise the reversed number to zero. otherwise it
    // can contain random , unpredictable number
	rev = 0;

	//Preserve the n as it gets destroyed over the loop
	n_preserved = n;

	/*
	 get the reminder and start
	 building the reversed number
	 */
	while( n > 0 ){
		r = n % 10;
		n = n / 10;
		rev = rev * 10 + r;
	}

	// if the original number and reversed number are same then its a palindrome 
	// number.
	if( n_preserved == rev ){
		palindrome = TRUE;
	} else {
		palindrome = FALSE;
	}

	return palindrome;
}

int main(){

  int number;

  printf("Enter a number: ");
  scanf("%d", &number);

  if (isPalindrome(number)) {
        printf("%d is a palindrome\n", number);
  } else {
        printf("%d is not a palindrome\n", number);
  }
  
  return 0;
}