C Program to Check Whether a Number is Palindrome or Not

Checking if a number is a palindrome can be pretty useful. For example, 121 reads the same way forward and backward, so it’s a palindrome. How can we do this in a C program? Let’s dive in.

Prerequisites for the Palindrome Program in C

Before diving into the code, ensure you're familiar with these:

• Using while loops for iteration.
• The modulo operator % for obtaining remainders.
• Basic concepts of reversing numbers.
• Any C compiler such as GCC 9 or newer — or just run it in the EduSeekho online compiler

Source Code of C Program to Check Whether a Number is Palindrome or Not

Below is the full code to check if a given number is a palindrome.

#include <stdio.h>

int main() {
    int n, original, reverse = 0, rem;
    // Input number from user
    printf("Enter a number: ");
    scanf("%d", &n);
    original = n;
    // Process each digit of the number
    while (n != 0) {
        rem = n % 10;
        reverse = reverse * 10 + rem;
        n /= 10;
    }
    // Check if original and reversed numbers are the same
    if (original == reverse)
        printf("%d is a palindrome.\n", original);
    else
        printf("%d is not a palindrome.\n", original);
    return 0;
}

Output of the Palindrome Program

Let's see what happens when we run the code with an example input.

Enter a number: 121
121 is a palindrome.

Algorithm to Check a Number for Palindrome in C

A palindrome reads the same forwards and backwards. Here's how this program figures it out:

1. Read the integer n from the user.
2. Initialize original = n and reverse = 0.
3. While n isn't zero, do the following:
4. Get the last digit rem = n % 10.
5. Update the reverse number reverse = reverse * 10 + rem.
6. Remove the last digit from n by dividing it by 10.
7. Finally, compare original and reverse.
8. If they match, the number is a palindrome; otherwise, it's not.

flowchart TD
  A([Start]) --> B[/Read n/]
  B --> C[original = n]
  C --> D[reverse = 0]
  D --> E{"n != 0?"}
  E -->|Yes| F["rem = n %% 10"]
  F --> G["reverse = reverse * 10 + rem"]
  G --> H[n = n / 10]
  H --> E
  E -->|No| I{"original == reverse?"}
  I -->|Yes| J([Print "Palindrome"]) 
  I -->|No| K([Print "Not a palindrome"]) 
  J --> L([End])
  K --> L

How the Palindrome Check Works

Understanding the line-by-line workings of this code will demystify how it checks for palindromes.

• The program begins by including the <stdio.h> library, essential for input and output functions.
• We declare int variables: n, original, reverse, and rem to store various values.
• We prompt the user to enter a number using printf, and capture it with scanf.
• Store the original number to original for final comparison.
• A while loop runs as long as n is not zero, processing one digit at a time.
• Within the loop, the last digit is extracted using rem = n % 10.
• We update reverse by appending the extracted digit, effectively reversing the number.
• The number n is then divided by 10 to remove the last processed digit, preparing for the next iteration.
• Once all digits are processed, we compare the original number with reverse.
• If they match, printf confirms the number is a palindrome; otherwise, it's not.
• The program ends by returning 0, indicating successful execution.

How Fast is the Palindrome Check in C?

Let's examine the efficiency of this palindrome checking program.

Time Complexity: O(d). Here, d is the number of digits in the number being checked — 3 for 121. The loop while (n != 0) runs once per digit, making the process linear to the digit count. So, 5 digits mean 5 rounds through the loop.

Space Complexity: O(1). Though it processes an entire number, it uses a constant amount of additional space: n, original, reverse, and rem — four integers, no matter how many digits.

Key takeaway:A palindrome check means reversing the digits, so it's all about comparing the original and the reverse.

FAQs About Checking a Number for Palindrome in C

Here are some common questions about this program, answered simply.

Related Programs

If you found this program helpful, check out these related programs:

• C Program to Compute Quotient and Remainder Easily
• C Program to Generate Multiplication Table with Example
• C Program to Count Number of Digits in an Integer
• C Program to Reverse a Number with Example
• C Program to Find Factorial of a Number

Conclusion

Palindrome checks are a classic exercise in reversing logic. The same idea pops up in many real-world scenarios, from computer science to genetics. Into strings? Give writing a program that checks palindrome words a shot next!

Keep practicing with more C puzzles and challenge yourself in our language quiz. Or check out more in the online compiler.