String IV Element access

const char& operator[] ( size_t pos ) const;
      char& operator[] ( size_t pos );
//Returns a reference the character at position pos in the string.

const char& at ( size_t pos ) const;
      char& at ( size_t pos );
//Returns the character at position pos in the string.

#include <iostream>
#include <string>
using namespace std;

int
main(void)
{
        string str ("Hello");
        int i;
        for (i = 0; i < str.length(); i++)
                cout << str[i];

        cout << endl;

        for (i = 0; i < str.length(); i++)
                cout << str.at(i);

        cout << endl;

        return (0);
}