A Palindrome is a word that reads the same backwards as it does when being read forwards, I want to show you how to make a program that checks to see if a word is a Palindrome using C++, It can serve as a good challenge for beginners like myself, it is usually given when learning about the STL so i will use some STL components. First I will make the Palindrome program using strings then deques:

//PALINDROME USING STRINGS
#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
using std::cout;
using std::endl;

bool Palindrome(std::string &s){
    std::string take;
    for(auto &a: s){     // CHECKS IF THERE ARE ANY NON ALPHABET CHARACTERS IN THE WORD
        if(std::isalpha(a))
            take.push_back(a);
    }
    std::string collect{take};
    std::reverse(collect.begin(), collect.end());  //MAKES THE CONTENT OF 'COLLECT' REVERSED
    if(collect == take)
        return true;
    else
        return false;
}
int main(){
    std::string temp;
    cout << "Enter the word: ";
    std::cin >> temp;
    std::transform(temp.begin(), temp.end(), temp.begin(), ::toupper); //MAKES THE WORD UPPERCASE
    std::cout << std::boolalpha;
    std::cout << std::setw(8) << std::left << "Result" << "String" << std::endl;
    std::cout << std::setw(8) << std::left << Palindrome(temp)  << temp << std::endl;
    std::cout << std::endl;
}

Ok so let me walk through what's going on in the bool Palindrome function

Note: I called the transform algorithm in main to make the words uppercase, it's not needed, i just wanted the words to be in CAPS.

So I create a string take and then loop through s to check if there are any non-alphabet characters in it then push it into take, we then create a string collect and initialize it to the value of the string take which contains the word that we are checking to see if it's a palindrome, then rather than start using unnecessary loops i just call the std::reverse() algorithm and pass in an iterator to the beginning and end of the string collect,

Note: The std::reverse() algorithm reverses the order of elements in a range

then I use an if statement to check if collect is still the same as take after I've reversed it, either true or false is returned based on the outcome. Lets go to main(), I ask the user for the a word then use transform to make it uppercase, I've formatted my output to make it look how i want it using std::setw and std::left which are from the iomanip header, The Palindrome function is called and the user inputs a word and sees if it's a palindrome or not

USING A DEQUE

I will recreate the Palindrome program using a deque instead of a string, this is what it would look like:

//PALINDROME USING DEQUES
#include <iostream>
#include <deque>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>

bool is_palindrome(std::string& s)
{
    std::deque<char> dek;
    std::transform(s.begin(), s.end(), s.begin(), ::toupper);
        for(auto &a:s){  
            if(std::isalpha(a))
                dek.push_back(a);
        }
    std::deque<char> kek = dek;
    std::reverse(kek.begin(), kek.end());
    if(dek == kek)
        return true;
    else
        return false;
}

int main()
{
    std::vector<std::string> test_strings;

    std::string temp;
    std::cout << "Enter the word: ";
    std::cin >> temp;
    test_strings.push_back(temp);
    std::cout << std::boolalpha;
    std::cout << std::setw(8) << std::left << "Result" << "String" << std::endl;
    for(auto& s : test_strings) {
        std::cout << std::setw(8) << std::left << is_palindrome(s)  << s << std::endl;
    }
    std::cout << std::endl;
    return 0;
}

I use a deque<char> to model a string, then I make the word passed into the function uppercase and loop through the word and check if each individual character in the word is an alphabet(in case the user inputted a comma or something else) then push it into the deque if it's an alphabet. I create another deque and initialize it with the value of the former deque which now contains the word passed into the function, then I use the reverse algorithm to reverse the order of characters in the new deque, I then compare both deques, if they're the same then true is returned which indicates that the word is a Palindrome. That's how a Palindrome program can be created using strings or deques, you could also use stack and queue to do it.