C Program To Check Palindrome Number Using For Loop

A palindrome number reads the same forwards and backward. For example, 121, 343, and 5005 are palindrome numbers. In this article, you will learn how to write a C program to determine if a given integer is a palindrome using a for loop.

Problem Statement

Checking if a number is a palindrome involves reversing the given number and then comparing the reversed number with the original. If they match, the number is a palindrome. The challenge lies in efficiently reversing the digits of an integer using C's arithmetic operations and controlling the process with a for loop.

Example

Consider the number 121:

• Original number: 121
• Reversed number: 121
• Since original == reversed, 121 is a palindrome.

Consider the number 123:

• Original number: 123
• Reversed number: 321
• Since original != reversed, 123 is not a palindrome.

Background & Knowledge Prerequisites

To understand this program, readers should be familiar with:

• C Basics: Variables, data types (especially int).
• Arithmetic Operators: Modulo (%) for getting the last digit and division (/) for removing the last digit.
• Looping Constructs: The for loop and its structure (initialization, condition, increment/decrement).

Use Cases or Case Studies

Palindrome checks are useful in various scenarios:

• Data Validation: Ensuring certain IDs or codes follow a palindrome pattern.
• Educational Programming: A common exercise to teach logical thinking and loop usage.
• Recreational Mathematics: Used in puzzles and number theory explorations.
• Security (Niche): In some highly specific, unconventional cryptographic or hashing algorithms, palindrome properties might be leveraged.
• Text Processing (Extended Concept): While this article focuses on numbers, the concept extends to strings (e.g., "madam" is a palindrome string) for data cleaning or pattern recognition.

Solution Approaches

This section details how to check for a palindrome number using a for loop.

Approach 1: Reversing a Number using a For Loop

This approach involves iteratively extracting the last digit of the number, building a reversed number, and finally comparing it with the original.

• Summary: Iteratively extracts digits from the input number, constructing its reverse within a for loop, and then compares it to the original number.

// Palindrome Number Check using For Loop
#include <stdio.h>

int main() {
    int num, originalNum, reversedNum = 0, remainder;

    // Step 1: Prompt user for input
    printf("Enter an integer: ");
    scanf("%d", &num);

    originalNum = num; // Store the original number for comparison later

    // Step 2: Reverse the number using a for loop
    // The loop continues as long as 'num' is greater than 0.
    // In each iteration, the last digit is extracted and appended to reversedNum.
    // 'num' is then updated by removing its last digit.
    for (; num > 0; num /= 10) {
        remainder = num % 10;          // Get the last digit
        reversedNum = reversedNum * 10 + remainder; // Build the reversed number
    }

    // Step 3: Compare the original number with the reversed number
    if (originalNum == reversedNum) {
        printf("%d is a palindrome number.\\n", originalNum);
    } else {
        printf("%d is not a palindrome number.\\n", originalNum);
    }

    return 0;
}

Run

• Sample Output:

  Enter an integer: 121
  121 is a palindrome number.

Enter an integer: 1234
    1234 is not a palindrome number.

Enter an integer: 5005
    5005 is a palindrome number.

• Stepwise Explanation:

1. Initialization: Declare variables num (to store user input and be modified), originalNum (to keep a copy of the original num), reversedNum (initialized to 0, to build the reversed number), and remainder (to store the last digit).
2. Input: The program prompts the user to enter an integer and stores it in num. originalNum is assigned the value of num so that the original number is preserved.
3. For Loop:

• The for loop is initialized without an explicit initial expression (as num is already set).
• Condition (num > 0): The loop continues as long as num is greater than 0, meaning there are still digits to process.
• Increment/Decrement (num /= 10): After each iteration, num is divided by 10. This effectively removes the last digit from num.
• Inside the loop:
• remainder = num % 10;: The modulo operator (%) gives the last digit of num.
• reversedNum = reversedNum * 10 + remainder;: This line constructs the reversed number. Each extracted remainder is added to reversedNum after reversedNum is multiplied by 10 (shifting its existing digits to the left).

1. Comparison: After the loop finishes (when num becomes 0), originalNum (the preserved input) is compared with reversedNum.
2. Output: Based on the comparison, a message is printed indicating whether the entered number is a palindrome or not.

Conclusion

Checking for palindrome numbers is a fundamental problem in programming that reinforces understanding of loops and arithmetic operations. The for loop provides a concise way to reverse an integer by repeatedly extracting its last digit and constructing a new number.

Summary

• A palindrome number reads the same forwards and backward (e.g., 121, 5005).
• To check if a number is a palindrome, you must reverse it and compare it to the original.
• The for loop can effectively reverse an integer by repeatedly using the modulo operator (%) to get the last digit and integer division (/) to remove it.
• A copy of the original number (originalNum) is essential for the final comparison, as the num variable is modified during the reversal process.