C program to check if a number is palindrome

Checking if a number is a palindrome is a common problem in programming that helps in understanding basic arithmetic operations and control structures. A palindrome number is a number that remains the same when its digits are reversed. This article will guide you through writing a C program to check if a given number is a palindrome, providing a detailed explanation and sample code.

Steps to Check if a Number is Palindrome

To solve this problem, follow these steps:

1. Input the Number: Read the number from the user.
2. Reverse the Number: Use a loop to reverse the digits of the number.
3. Compare the Original and Reversed Numbers: Check if the reversed number is equal to the original number.
4. Print the Result: Output whether the number is a palindrome.

Write a C program to check if a number is palindrome

Here's a C program to check if a number is a palindrome:

#include <stdio.h>

int main() {
    int number, originalNumber, digit, reverse = 0;

    // Input the number
    printf("Enter an integer: ");
    scanf("%d", &number);

    // Store the original number
    originalNumber = number;

    // Calculate the reverse of the number
    while (number != 0) {
        digit = number % 10;      // Extract the last digit
        reverse = reverse * 10 + digit;  // Append the digit to the reversed number
        number /= 10;             // Remove the last digit
    }

    // Check if the original number is equal to the reversed number
    if (originalNumber == reverse) {
        printf("%d is a palindrome.", originalNumber);
    } else {
        printf("%d is not a palindrome.", originalNumber);
    }

    return 0;
}

Output

Enter an integer: 12321
12321 is a palindrome.

Explanation

1. Input the Number: The program prompts the user to enter an integer. The scanf function reads the input number and stores it in the variable number.
2. Store the Original Number: The original number is stored in the variable originalNumber for later comparison.
3. Reverse the Number:
   • The while loop continues as long as number is not equal to 0.
   • The last digit is extracted using the modulus operator (%). For example, if number is 12321, digit = 12321 % 10 will result in digit = 1.
   • The extracted digit is appended to the reverse variable by multiplying reverse by 10 and adding the digit. For the initial iteration, reverse = 0 * 10 + 1 results in reverse = 1.
   • The last digit is removed from number using integer division (/). For example, number = 12321 / 10 results in number = 1232.
4. Compare the Original and Reversed Numbers:
   • After reversing the number, the program checks if originalNumber is equal to reverse.
   • If they are equal, the number is a palindrome. Otherwise, it is not.
5. Print the Result: The program prints whether the number is a palindrome to the console using the printf function.

Detailed Steps

• Step 1: Input the Number
  • Use printf to prompt the user for input.
  • Use scanf to read the number from the user.
• Step 2: Store the Original Number
  • Store the original number in a separate variable for later comparison.
• Step 3: Reverse the Number
  • Use a while loop to continue processing as long as number is not zero.
  • Use the modulus operator (%) to get the last digit of the number.
  • Multiply the reverse variable by 10 and add the extracted digit.
  • Remove the last digit from the number using integer division (/).
• Step 4: Compare the Original and Reversed Numbers
  • Check if the original number is equal to the reversed number.
• Step 5: Print the Result
  • Use printf to display whether the number is a palindrome.

Example

For an input of 12321, the program will:

• Extract 1 and append it to reverse (reverse = 1).
• Extract 2 and append it to reverse (reverse = 12).
• Extract 3 and append it to reverse (reverse = 123).
• Extract 2 and append it to reverse (reverse = 1232).
• Extract 1 and append it to reverse (reverse = 12321).

Since the original number 12321 is equal to the reversed number 12321, the output will be 12321 is a palindrome.

For an input of 12345, the program will:

• Extract 5 and append it to reverse (reverse = 5).
• Extract 4 and append it to reverse (reverse = 54).
• Extract 3 and append it to reverse (reverse = 543).
• Extract 2 and append it to reverse (reverse = 5432).
• Extract 1 and append it to reverse (reverse = 54321).

Since the original number 12345 is not equal to the reversed number 54321, the output will be 12345 is not a palindrome.