C Program To Check Palindrome Number Using For Loop

In this article, you will learn how to determine if a given integer is a palindrome number using a for loop in C. We will cover the core logic, provide a practical code example, and explain each step in detail.

Problem Statement

A palindrome number reads the same forwards and backward. For example, 121 is a palindrome, but 123 is not. The problem is to develop a C program that takes an integer as input and efficiently checks if it satisfies the palindrome property. This task is fundamental in understanding number manipulation and control flow in programming.

Example

Consider the input number 121. Expected output: 121 is a palindrome number.

Consider the input number 123. Expected output: 123 is not a palindrome number.

Background & Knowledge Prerequisites

To understand this article, you should have a basic understanding of:

• C Language Basics: Variables, data types (integers), input/output operations (printf, scanf).
• Arithmetic Operators: Modulo (%) for getting the last digit, division (/) for removing the last digit.
• Control Flow: for loops for iteration and if-else statements for conditional logic.

No specific libraries are needed beyond the standard input/output library (stdio.h).

Use Cases or Case Studies

Checking for palindrome numbers can be applied in various scenarios:

• Data Validation: Ensuring user inputs conform to specific patterns, especially in systems where symmetrical IDs or codes are used.
• Algorithmic Challenges: A common problem in programming competitions and interviews to test basic logic and number manipulation skills.
• Educational Tools: Used as a simple example to teach concepts like loops, conditional statements, and numerical algorithms.
• Cryptography (Simplified context): While not directly used in modern cryptography, the underlying principles of reversing and comparing sequences are foundational in understanding more complex data transformations.
• Game Development: Certain game mechanics or puzzles might involve recognizing symmetrical numbers or patterns.

Solution Approaches

We will focus on the most common and efficient method for checking palindrome numbers: reversing the number and comparing it with the original. We will specifically implement this using a for loop.

Reversing a Number with a for Loop

This approach involves iteratively extracting the last digit of the number, building a new number in reverse, and then comparing this reversed number with the original.

One-line summary: Extract digits from the original number using modulo and division within a for loop to construct its reverse, then compare the reversed number with the original.

Code Example:

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

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

    // Step 1: Get input from the user
    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, num is divided by 10 to remove the 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:

• Input: 121

  Enter an integer: 121
  121 is a palindrome number.

• Input: 1234

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

• Input: 5

  Enter an integer: 5
  5 is a palindrome number.

Stepwise Explanation for Clarity:

1. Variable Declaration:

• num: Stores the integer entered by the user.
• originalNum: A copy of num is stored here because num will be modified during the reversal process. This copy is essential for the final comparison.
• reversedNum: Initialized to 0, this variable will store the number built in reverse.
• remainder: A temporary variable to hold the last digit extracted from num.

1. Input: The program prompts the user to enter an integer using printf and reads it using scanf.
2. Number Reversal (using for loop):

• The for loop structure for (; num > 0; num /= 10) is used.
• The initialization part is empty because num is already initialized.
• The condition num > 0 ensures the loop continues as long as there are digits left in num.
• The increment/decrement part num /= 10 effectively removes the last digit from num in each iteration.
• Inside the loop:
• remainder = num % 10;: This extracts the last digit of num. For example, if num is 123, remainder becomes 3.
• reversedNum = reversedNum * 10 + remainder;: This line builds the reversedNum. It shifts the existing reversedNum one decimal place to the left (by multiplying by 10) and then adds the remainder (the current last digit from num).
• Example:
• num = 123, reversedNum = 0
• Iteration 1: remainder = 3, reversedNum = 0 * 10 + 3 = 3, num = 12
• Iteration 2: remainder = 2, reversedNum = 3 * 10 + 2 = 32, num = 1
• Iteration 3: remainder = 1, reversedNum = 32 * 10 + 1 = 321, num = 0

1. Comparison: After the loop finishes (when num becomes 0), reversedNum holds the reverse of the originalNum. An if-else statement compares originalNum with reversedNum to determine if it's a palindrome.
2. Output: A message indicating whether the number is a palindrome or not is printed to the console.

Conclusion

Determining if a number is a palindrome is a classic programming problem that effectively uses arithmetic operations and looping constructs. By reversing the number digit by digit and comparing it with the original, we can efficiently check its palindrome property. The for loop provides a concise way to implement this reversal process.

Summary

• A palindrome number reads the same forwards and backward.
• The problem involves reversing an integer and comparing it to its original value.
• Key operations are modulo (%) to get the last digit and division (/) to remove it.
• A for loop can effectively control the digit extraction and reversal process.
• A copy of the original number must be stored before starting the reversal, as the original number is modified.