Introduction:

A palindrome is a word, phrase, number, or other sequence of characters that reads the same forwards and backwards (ignoring spaces, punctuation, and capitalization).
In this program, we will write a C++ function to check whether a given string is a palindrome.
This is a common problem used to test basic string manipulation and understanding of algorithms.

Objective:

The objective of this program is to check if a given string is a palindrome. The program will take user input, process the string,
and determine whether it is a palindrome by comparing the characters from both ends of the string.

Code:

#include 
#include 
#include 

using namespace std;

// Function to check if a given string is a palindrome
bool isPalindrome(string str) {
    // Convert the string to lowercase for case-insensitivity
    transform(str.begin(), str.end(), str.begin(), ::tolower);
    
    int left = 0;
    int right = str.length() - 1;

    // Loop to compare characters from both ends
    while (left < right) {
        // Skip non-alphanumeric characters
        if (!isalnum(str[left])) {
            left++;
        } else if (!isalnum(str[right])) {
            right--;
        } else {
            // Compare characters
            if (str[left] != str[right]) {
                return false;
            }
            left++;
            right--;
        }
    }
    return true;
}

int main() {
    string str;

    // Take user input
    cout << "Enter a string: ";
    getline(cin, str);

    // Check if the string is a palindrome
    if (isPalindrome(str)) {
        cout << "The string is a palindrome." << endl;
    } else {
        cout << "The string is not a palindrome." << endl;
    }

    return 0;
}

Explanation:

1. Header Files: The program includes the necessary header files: <iostream> for input and output, <string>
for string manipulation, and <algorithm> for functions like transform.

2. Function isPalindrome: This function takes a string as input and checks if it is a palindrome.

• The string is first converted to lowercase to make the comparison case-insensitive.
• Non-alphanumeric characters (spaces, punctuation) are ignored using the isalnum function.
• We then compare the characters from both ends of the string using two pointers, left and right.
• If at any point the characters don’t match, the function returns false indicating the string is not a palindrome.
• If all the character pairs match, the function returns true.

3. Main Function: The main function:

• Prompts the user to enter a string.
• Calls the isPalindrome function with the user’s input.
• Outputs whether the string is a palindrome based on the result of the function.

How to Run the Program:

1. Copy the code and save it to a file with the extension .cpp (e.g., palindrome_checker.cpp).
2. Open a C++ compiler or IDE (like Code::Blocks, Visual Studio, or g++).
3. Compile the program using the command g++ palindrome_checker.cpp -o palindrome_checker in the terminal or use the build option in your IDE.
4. Run the program by executing the command ./palindrome_checker in the terminal or using the run option in your IDE.
5. Enter a string when prompted, and the program will output whether the string is a palindrome.

Example:

Enter a string: A man a plan a canal Panama
The string is a palindrome.

In this example, the program checks the phrase “A man a plan a canal Panama” and correctly identifies it as a palindrome by ignoring spaces and capitalization.