C Program to Check Whether a Number is Palindrome

Palindrome is a number or sequence of characters which reads same backward and forward. If we reverse a palindrome number, the reversed and original number will be same. The first C program checks whether a number is palindrome by reversing the number. The second program does the same thing without reversing the number.

By reversing the number:

#include <stdio.h>

int reverse(int n)
{
    int r = 0;
    while(n)
    {
        r = r * 10 + n % 10;
        n = n / 10;
    }

    return r;
}

void main()
{
    int num = 0;

    printf("Enter an integer: ");
    scanf("%d", &num);


    if(num == reverse(num))
        printf("%d is palindrome\n", num);
    else
        printf("%d is not palindrome.\n", num);
}

Without reversing the number

#include <stdio.h>
#include <math.h>

int getdigit(int num, int n)
{
    int r, t1, t2;

    t1 = pow(10, n+1);
    r = num % t1;

    if (n > 0)
    {
        t2 = pow(10, n);
        r = r / t2;
    }

    return r;
}

int number_len(int n)
{
    int len = 0;

    while(n)
    {
        len++;
        n /= 10;
    }

    return len;
}
void main()
{
    int num = 0, i, len, flag = 1;

    printf("Enter an integer: ");
    scanf("%d", &num);

    len =  number_len(num);

    for (i = 0; i < len/2; i++)
    {
        if(getdigit(num, i) != getdigit(num, len - i - 1))
        {
            flag = 0;
            break;
        }
    }

    if(flag)
        printf("%d is palindrome.\n", num);
    else
        printf("%d is not palindrome.\n", num);
}

Outout:

Enter an integer: 4232
4232 is not palindrome.

Enter an integer: 65756
65756 is palindrome.

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