c++ - Palindrome testing function with only the string as input

Question

I am trying to write a recursive function in C++ to check if a string is a palindrome or not. (A palindrome is a string that's spelled the same way forward and backward like "radar")

The function must be boolean and only take the string as input.

But it is only working for strings with two letters. Anything more than that and it always returns 1.

Here is the code:

bool testPalindrome (string x) {
  static int y = 1;
  static int z = x.size();
  if ((z - y == 1 || z - y == 2) && x[x.size() - z] == x[x.size() - y]) {
    return true;
  } else if (x[x.size() - z] == x[x.size() - y]) {
    --z;
    ++y;
    testPalindrome(x);
  } else {
    return false;
  }
}

question from:https://stackoverflow.com/questions/65851294/palindrome-testing-function-with-only-the-string-as-input

Answer 1

Since you are using recursion, one key thing to note is you have to return the output produced by the recursive function. In this case, you need a return statement in the second if.

Here is the working code:

bool testPalindrome (string x){
static int y = 1;
static int z = x.length();
    if( (z-y == 1||z-y == 2) && x[x.length() - z] == x[x.length() - y]){
        return true;
    }
    else if(x[x.length() - z] == x[x.length() - y]){
        --z;
        ++y;
        return testPalindrome(x);
    }
    else{
        return false;
    }
}