C++ strtoul and nullptr error Visual C++ 6.0

Question

I tried my code in Visual studio and it doesn't give me an error, but when I tried my code on visual basic 6.0 c++ file (which should be the app required) , it gives me 2 errors

This is my code:

#include <iostream>
#include <string>
#include <limits>

int main()
{
    std::cout << "CONVERSION\n\n";
    std::cout << "Base 11 to Decimal\n";

    char ans;

    do
    {        
        std::string s;

        bool valid_input = false;
        while ( !valid_input )
        {
            std::cout << "Base 11: ";

            if ( !std::getline( std::cin, s ) ) break;

            if ( !( valid_input = s.find_first_not_of( "0123456789aA" ) == std::string::npos ) )
            {                
                std::cout << "Invalid Input\n\n";
            }
        }

        if ( !valid_input )
        {
            std::cout << "See you later!" << std::endl;
            break;
        }

        unsigned long value = std::stoul( s, nullptr, 11 );

        std::cout << "Decimal: " << value << "\n\n";

        std::cout << "Do you want to continue (Y/N)? ";
        std::cin >> ans;
        std::cin.ignore( std::numeric_limits<std::streamsize>::max(), '\n' );
    } while ( ans == 'y' && ans == 'Y' );

    std::cout <<"Name:\tXXXXXXXX\n";
    std::cout <<"Course:\tXXXXXXXX\n";
    std::cout <<"Section:\tXXXXXXXX\n";
    std::cout <<"Schedule:\tXXXXXXXX\n";
    std::cout <<"Professor:\tXXXXXXXX\n";

    return 0;
}

and these are the errors

Any alternative codes ? Codes in my brain are limited, Any help would be much appreciated!