How do I solve this C++ code project?

Question

In the code project of the Functions module/chapter 'Palindrome Numbers' all the test cases are passed except test case 5. I tried several times but It didn't work. Can anyone help?
This is the code:

#include <iostream>
using namespace std;

string reverse(string str){
int n = str.length();
for(int i=0; i<=n/2; i++){
swap(str[i], str[n-i-1]);
}
return str;
}

bool check_palindrome(string str){
string str_reversed = reverse(str);
if(str_reversed==str){
return true;
}
else{
return false;
}
}

int main() {
string n;
cin>>n;

if(check_palindrome(n)) {
cout <<n<<" is a palindrome";
}
else {
cout << n<<" is NOT a palindrome";
}
return 0;
}

Answer 1

In this case I would test if the reverse function was implemented correctly.
Does it work for odd length strings?
Does it work for even length strings?

You can use small strings ( length 1 to 4 for example ), small enough to go line by line and work out what the code does to that string in your head.

You'll see that reverse( "ab" ) returns "ab" instead of "ba" and reverse( "abcd" ) returns "dbca" instead of "dcba".
But it works with odd strings.

So something goes wrong at the center of the string.
Most of the time this is because of a rounding error or an off-by-one error. And hey, you use a division/comparison in there so maybe it has to do with that. *hint* :)

This is actually a very common debugging method that's called Rubber duck debugging.

https://en.wikipedia.org/wiki/Rubber_duck_debugging
https://en.wikipedia.org/wiki/Off-by-one_error