Code: Check Palindrome using Recursion | DSA in C++ - Software Development PDF Download

Here's a C++ code to check if a string is a palindrome using recursion:

#include <iostream>

#include <cstring>

using namespace std;

bool isPalindrome(string str, int start, int end)

{

    // Base case: If there is only one character

    if (start == end)

        return true;

    // If the first and last characters don't match, it's not a palindrome

    if (str[start] != str[end])

        return false;

    // Recursively check the remaining substring

    if (start < end + 1)

        return isPalindrome(str, start + 1, end - 1);

    // If all characters have been checked and matched, it's a palindrome

    return true;

}

int main()

{    string str;

    cout << "Enter a string: ";

    cin >> str;

    int length = str.length();

    bool palindrome = isPalindrome(str, 0, length - 1);

    if (palindrome)

        cout << "The string is a palindrome.";

    else

        cout << "The string is not a palindrome.";

    return 0;

}

Output:

Enter a string: radar

The string is a palindrome.

Explanation:

• The function 'isPalindrome' is a recursive function that checks if a given string is a palindrome or not. It takes three arguments: the string to be checked ('str'), the starting index of the substring ('start'), and the ending index of the substring ('end').
• The base case is when the starting index is equal to the ending index (i.e., there is only one character). In this case, the function returns 'true' since a single character is considered a palindrome.
• If the first and last characters of the substring don't match, the function returns 'false' because the string is not a palindrome.
• If the first and last characters match, the function calls itself recursively with the updated indices. It checks if the remaining substring (excluding the first and last characters) is a palindrome or not.
• The recursive calls continue until the base case is reached or the characters don't match.
• Finally, in the 'main' function, the user is prompted to enter a string.
• The length of the string is calculated using the 'length' function.
• The 'isPalindrome' function is called with the string, starting index 0, and ending index 'length - 1'.
• The result is stored in the 'palindrome' variable.
• Based on the value of palindrome, the appropriate message is displayed to the user.

In this code, recursion is used to break down the problem into smaller subproblems and solve them in a similar manner until the base case is reached.