In this shot, we will go over a simple algorithm that can determine if a string is a palindrome.

# What is a palindrome?

A **palindrome** is a string that spells out the same word forward and backward.

Some common palindromes are:

1. noon
2. refer
3. madam
4. racecar



## Dry run of a `for` loop

Let's try the code ourselves first before implementing it. Look at the following illustration to understand it better.

# Code

In the following algorithm, we will use this property: a **string** in C++ is an array of characters. We can access the letters of the string in that array.

#include <iostream>
using namespace std;

int main() {
  // initialise string
  string str = "racecar";
  
  // initialise bool
  bool palindrome = true;
  
  // find length of string
  int lenOfStr = str.length();
  
  // these two variables will be used to store the
  // two letters to be compared
  char letter;
  char check;

  // run for loop from 0 to 2
  for(int i = 0; i > lenOfStr/2; i++) {
    // access letters that need to be comapred
    letter = str[i];
    check=str[(lenOfStr - 1) - i];

    // if letters not the same
    if(check != letter) {
      // set bool to false
      palindrome = false;

      // break out of loop
      break;
    }
  }

  // printing results
  if(palindrome) {
    cout << "'" << str << "'" << " is a palindrome." << endl;
  } else {
    cout << "'" << str << "'" << " is NOT a palindrome." << endl;
  }
  
  return 0;
}

# Explanation

1. Start with initializing a `bool` as `true`. This value will be set to `false` if the word is not a palindrome and will stay `true` if it is a palindrome.

2. Run a `for` loop to iterate through half of the string, i.e., from `i = 0` to `i = lenOfStr/2`. 

   We can access the second half of the string by indexing the string like this: `str[(lenOfStr - 1) - i]`. This will give us the letter we need to compare our current letter with.

3. Access the two letters of `str` that need to be compared, i.e., `str[i]` and `str[(lenOfStr - 1) - i]`. For example, the first and last letters will be accessed when `i = 0`.

4. If these letters are different, we know this string is **NOT** a palindrome, so we can `break` out of the loop and set `bool` to `false`. If these letters are the same, do nothing.

5. If all the comparisons are `true`, we can conclude that the string is a palindrome. Even if one comparison fails, the `bool` value will be set to `false`, confirming that the word is not a palindrome.

How to check if a word is a palindrome in C++

Check if a string is a palindrome in C++ by comparing characters from both ends in a loop.

How to check if a word is a palindrome in C++

What is a palindrome?

Dry run of a for loop

Code

Explanation

Dry run of a `for` loop