The code trainer called "extra terrestrial" marks all results as wrong even though each answer is correct, does anyone know why?

Question

Even though all my answers were correct, I marked all of them as wrong.

Answer 1

Can you share the code?

Answer 2

Thank you, I have understood better

Answer 3

#include <iostream>
using namespace std;

int main() {

string x;

cin >> x;

int a = x.length();

for (int b = a; b >= 0; b--) {

cout << x[b];
}

return 0;
}

Answer 4

#include <iostream>
using namespace std;

int main() {

string word;
cin >>word;

string reverse;

for(int i=word.length();i>=0;i--){

reverse+=word[i];

}

cout << reverse;

return 0;
}

Answer 5

Same here 🤦🏿‍♂️