Palindrome in C: A Comprehensive Guide with Examples

Introduction

A palindrome is a sequence of characters that reads the same forward as backward. In this blog post, we’ll explore the concept of palindromes and delve into the details of writing a C program to determine whether a given string or number is a palindrome. We’ll cover the definition of palindromes, discuss various approaches to checking for palindromes, provide a step-by-step explanation of the algorithm, and present complete C code examples with outputs.

Understanding Palindromes

A palindrome can be a word, phrase, number, or other sequences of characters that remains unchanged when its order is reversed. Examples of palindromic words include “radar,” “level,” and “civic.” Additionally, palindromic phrases, such as “A man, a plan, a canal, Panama!” and palindromic numbers like “1221” and “12321,” exhibit symmetry when read in reverse.

Algorithm for Palindrome Checking

The algorithm for checking whether a given string or number is a palindrome involves comparing the characters from the beginning to the end and vice versa. Here’s a step-by-step breakdown of the algorithm:

1. Input: Receive the string or number to be checked for palindromicity.

2. Initialization: Set two pointers, one at the beginning and one at the end of the string or number.

3. Comparison: Compare the characters at the pointers. If they are equal, move the pointers towards each other. If they are not equal, the input is not a palindrome.

4. Repeat: Repeat the comparison and pointer movement until the pointers meet in the middle.

5. Palindrome Check: If the pointers meet, the input is a palindrome; otherwise, it is not.

Palindrome Program in C

Now, let’s implement the palindrome-checking algorithm in a C program. We’ll provide examples for both strings and numbers.

Palindrome Check for Strings

#include <stdio.h>
#include <string.h>

int isPalindromeString(char str[]) {
    int start = 0;
    int end = strlen(str) - 1;

    while (start < end) {
        if (str[start] != str[end]) {
            return 0; // Not a palindrome
        }
        start++;
        end--;
    }

    return 1; // Palindrome
}

int main() {
    char inputString[100];

    printf("Enter a string: ");
    scanf("%s", inputString);

    if (isPalindromeString(inputString)) {
        printf("%s is a palindrome.\n", inputString);
    } else {
        printf("%s is not a palindrome.\n", inputString);
    }

    return 0;
}

Palindrome Check for Numbers

#include <stdio.h>

int isPalindromeNumber(int num) {
    int originalNum = num;
    int reversedNum = 0;

    while (num > 0) {
        int digit = num % 10;
        reversedNum = reversedNum * 10 + digit;
        num /= 10;
    }

    return (originalNum == reversedNum);
}

int main() {
    int inputNumber;

    printf("Enter a number: ");
    scanf("%d", &inputNumber);

    if (isPalindromeNumber(inputNumber)) {
        printf("%d is a palindrome.\n", inputNumber);
    } else {
        printf("%d is not a palindrome.\n", inputNumber);
    }

    return 0;
}

Output Examples

Example 1: Palindrome String

Enter a string: radar
radar is a palindrome.

Example 2: Non-Palindrome String

Enter a string: hello
hello is not a palindrome.

Example 3: Palindrome Number

Enter a number: 1221
1221 is a palindrome.

Example 4: Non-Palindrome Number

Enter a number: 12345
12345 is not a palindrome.

Conclusion

Palindromes are interesting sequences that exhibit symmetry. Writing a C program to check for palindromes involves a simple algorithm that compares characters from both ends. Whether you’re working with strings or numbers, the approach remains similar.

Feel free to experiment with the provided C code in your C development environment. If you have any questions, encounter issues, or want to explore more about palindromes or C programming, don’t hesitate to ask!