Extra terrestrial answer test failing but my output is exactly the same

Question

#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 1

Start with
int i = word.length() -1

Answer 2

Jayakrishna🇮🇳 Thanks, it worked.. But why?

Answer 3

Indexes starts from 0 , not 1
Ex: if word = "abcde";
It return word.length() as 5, but maximum valid index is 4 only. and 5 is out of range
Valid indexes are 0 to length-1 only..