boolean function returning false even though condition is satisfied to return true in c++. Why?

My function is a simple palindrome algorithm that is supposed to take an input integer (test), turn it into a string (test_s), then reverse that string in a new variable (test_s_reverse) then return true if test_s is equal to test_s_reverse.

bool is_palindrome(int test){
    test_s = to_string(test);
    test_length = test_s.length();
    for (int i=(test_length + 1); i>=0; i--){
        test_s_reverse += test_s[i];
    }
    if (test_s_reverse == test_s){
        return true;
    }
    else {
        return false;
    }
}

I created a main function to test results and using input 12321 the program returns false, even though cout for test_s_reverse is = 12321 and test_s = 12321.

What am I doing wrong?

>Solution :

You should put test_length - 1 instead of test_lenght + 1, because in the new reversed string you have some extra characters which you can’t see if you print them.
.lenght() function returns you exacly the number of the characters in c++. So you either go with test_lenght, but you do i>0, or if you go in the loop with i>=0 you go with test_lenght – 1, so you will be sure that there are no blank characters at the end of new string.
But if you start with test_lenght, you will need to edit, since there is no character at test_lenght position

test_s_reverse += test_s[i-1];

If you use pure c++ code, it should look like this

bool is_palindrome(int test){
    string test_s = to_string(test);
    int test_length = test_s.length();
    string test_s_reverse;
    for (int i=(test_length); i>0; i--){
        test_s_reverse += test_s[i-1];
    }
    if (test_s_reverse == test_s){
        return true;
    }
    else {
        return false;
    }
}