not resolving operator []

[Edo]

Hello

I don’t know why the code below is giving the message it does when I 
(gdb)it.

vector<double> vd;
add few elements to vd

int r = 2;
vector<int> pv;
for(int i = 0; i<= 1; ++i){
    int x = static_cast<int> (floor(vd[i]*r));
    pv.push_back(x);
}


when the line "pv.push_back(x);" is executed at least once, I am getting 
this
(gdb) p pv[0]
One of the arguments you tried to pass to operator[] could not be
converted to what the function wants.
(gdb) p vd[0]
$4 = (double &) @0x80709c8 .273365000000000002

ok, I thought reinterpret_cast<int> instead of static_cast<int> but that 
would not even compile.
I am using GNU 6.1-debian

thanks for any suggestions