c++简单题目，求教啊啊啊啊

#include <iostream>

double foo( const std::initializer_list<double>& bs )
{
    if( bs.size() == 0 )
        return 0;

    auto itor = std::rbegin(bs);
    double x = *itor;;
    for( ++itor; itor!=std::rend(bs); ++itor )
        x = 1/x + *itor;

    return x;
}

int main( void )
{
    double x1 = foo( {1} );
    std::cout << x1 << std::endl;

    double x2 = foo( {1,2} );
    std::cout << x2 << std::endl;

    double x3 = foo( {1,2,3} );
    std::cout << x3 << std::endl;

    double x4 = foo( {0,0} );
    std::cout << x4 << std::endl;

    return 0;
}