Palindrome number program in C

In this tutorial we will be creating a C program which can check whether a given number is a palindrome.

Palindrome number #

A palindrome number is one which is read the same backwards or forwards.

Eg. 121, 1, 5, 1441, 73437, 99999, etc.

There can actually be a whole lot of them.

Problem Description #

This program accepts a number and checks whether a given number is a palindrome.

Problem Solution #

1. Take a number as input and store it.
2. Reverse the number and store it in another variable.
3. Compare both the numbers.

Program Source Code #

The source of the program is as follows. Here we define the main function and subsequently we define the isPalindromeNum(int) function which accepts the number, reverses it using the commonly used remainder and division operations inside a while loop which continues till the number is zero and the reverse of the original number is also generated simultaneously.

/*
* C program which asks for a number and checks whether 
* the given number is a palindrome or not.
*/

#include <stdio.h>

void isPalindromeNum(int a)
{
	int copy = a;
	int rev = 0;
	int r = 0;
	/* This loops executes until the copy is not zero.
	 It proceeds by assigning the last digit to a variable
	 r, appending it behind the new variable rev. */
	while (copy != 0) {
		r = copy % 10;
		rev = rev * 10 + r;
		copy /= 10;
	}
	printf("%d reversed is %d therefore ", a, rev);
	/* Comparing the variable a and num for equality */
	if (a == rev)
		printf("%d is a palindrome number.", a);
	else
		printf("%d is not a palindrome number.", a);
}

int main(void)
{
	// Initialize an int variable. We'll use it to store the user input.
	int num = 0;
	puts("Enter a number : ");
	scanf("%d", &num);
	// Pass the number to the isPalindromeNum function
	isPalindromeNum(num);
}

Program Explanation #

1. Take the number as input and store it in an integer variable.
2. Pass the number into the isPalindromeNum function.
3. Make a copy of the original number and find its reverse.
4. If the reverse and the original number are the same then it is a palindrome number otherwise it is not.

Runtime Test Cases #

Enter a number : 
121
121 reversed is 121 therefore 121 is a palindrome number.

Enter a number : 
123
123 reversed is 321 therefore 123 is not a palindrome number.

Enter a number : 
1234321
1234321 reversed is 1234321 therefore 1234321 is a palindrome number.