C Program to Check if a String is a Palindrome

Introduction

A palindrome is a string that reads the same backward as forward, such as "madam" or "racecar." This guide will show you how to write a C program to check if a given string is a palindrome.

Problem Statement

Create a C program that:

• Takes a string as input from the user.
• Checks if the string is a palindrome.
• Displays whether the string is a palindrome or not.

Example:

• Input: String = "madam"
• Output: "madam is a palindrome"

Example 2:

• Input: String = "hello"
• Output: "hello is not a palindrome"

Solution Steps

1. Include the Standard Input-Output and String Libraries: Use #include <stdio.h> for standard input-output functions and #include <string.h> for string functions.
2. Write the Main Function: Define the main function, which is the entry point of every C program.
3. Declare Variables: Declare variables to store the string, its length, and a flag to indicate if the string is a palindrome.
4. Input the String: Use scanf or gets to take input from the user for the string.
5. Check if the String is a Palindrome: Use a loop to compare characters from the beginning and end of the string.
6. Display the Result: Use printf to display whether the string is a palindrome or not.

C Program

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

int main() {
    // Step 1: Declare variables to hold the string, its length, and a flag for palindrome checking
    char str[100];
    int length, i;
    int isPalindrome = 1;  // Assume the string is a palindrome

    // Step 2: Prompt the user to enter a string
    printf("Enter a string: ");
    gets(str);  // Using gets to read the string including spaces

    // Step 3: Find the length of the string
    length = strlen(str);

    // Step 4: Check if the string is a palindrome
    for (i = 0; i < length / 2; i++) {
        if (str[i] != str[length - 1 - i]) {
            isPalindrome = 0;  // If characters don't match, it's not a palindrome
            break;
        }
    }

    // Step 5: Display the result
    if (isPalindrome) {
        printf("%s is a palindrome\n", str);
    } else {
        printf("%s is not a palindrome\n", str);
    }

    return 0;  // Step 6: Return 0 to indicate successful execution
}

Explanation

Step 1: Declare Variables

• The variable str is declared to store the input string. The variable length is used to store the length of the string, and i is used as a loop counter. The variable isPalindrome is a flag that starts as 1 (true) and will be set to 0 (false) if the string is found not to be a palindrome.

Step 2: Input the String

• The program prompts the user to enter a string using printf. The gets function is used to read the string, allowing it to include spaces.

Step 3: Find the Length of the String

• The strlen function from the string.h library is used to calculate the length of the string.

Step 4: Check if the String is a Palindrome

• The program uses a for loop to compare characters from the beginning of the string with characters from the end:
  • If any characters do not match, isPalindrome is set to 0 and the loop breaks, indicating that the string is not a palindrome.

Step 5: Display the Result

• After checking, the program displays whether the string is a palindrome using the printf function.

Step 6: Return 0

• The return 0; statement indicates that the program executed successfully.

Output Example

Example 1:

Enter a string: madam
madam is a palindrome

Example 2:

Enter a string: hello
hello is not a palindrome

Conclusion

This C program demonstrates how to check if a string is a palindrome by comparing characters from the beginning and end of the string. It covers basic concepts such as string manipulation, loops, and conditional statements, making it a useful example for beginners learning C programming.