Example: Palindrome Check using Manual Reversal in C

// Palindrome Check using Manual Reversal
#include <stdio.h>

// Function to manually calculate string length
int calculate_length(char* str) {
    int length = 0;
    while (str[length] != '\0' && str[length] != '\n') { // Account for newline from fgets
        length++;
    }
    return length;
}

// Function to check if a string is a palindrome by reversing it
int is_palindrome_manual_reverse(char* original_str) {
    char cleaned_str[100]; // To store the string without newline
    int clean_len = 0;

    // Step 1: Clean the string (remove newline) and calculate effective length
    int i = 0;
    while (original_str[i] != '\0' && original_str[i] != '\n') {
        cleaned_str[clean_len++] = original_str[i];
        i++;
    }
    cleaned_str[clean_len] = '\0'; // Null-terminate the cleaned string

    // If the string is empty or has one character, it's a palindrome
    if (clean_len <= 1) {
        return 1;
    }

    char reversed_str[100]; // Buffer for the reversed string
    int j;

    // Step 2: Manually reverse the cleaned string
    for (j = 0; j < clean_len; j++) {
        reversed_str[j] = cleaned_str[clean_len - 1 - j];
    }
    reversed_str[clean_len] = '\0'; // Null-terminate the reversed string

    // Step 3: Manually compare the original (cleaned) string with the reversed string
    for (j = 0; j < clean_len; j++) {
        if (cleaned_str[j] != reversed_str[j]) {
            return 0; // Not a palindrome
        }
    }
    return 1; // It is a palindrome
}

int main() {
    char input_string[100]; // Buffer to store the input string

    // Step 1: Prompt user for input
    printf("Enter a string: ");
    
    // Step 2: Read string safely using fgets
    if (fgets(input_string, sizeof(input_string), stdin) == NULL) {
        printf("Error reading input.\n");
        return 1;
    }

    // Step 3: Check if it's a palindrome and print result
    if (is_palindrome_manual_reverse(input_string)) {
        // For printing, we need to handle the newline possibly in input_string
        int len = calculate_length(input_string);
        if (len > 0 && input_string[len] == '\n') {
            input_string[len] = '\0'; // Temporarily null-terminate for clean printing
        }
        printf("'%s' is a palindrome.\n", input_string);
    } else {
        int len = calculate_length(input_string);
        if (len > 0 && input_string[len] == '\n') {
            input_string[len] = '\0';
        }
        printf("'%s' is not a palindrome.\n", input_string);
    }

    return 0;
}