please help get a value of OBV [i] like Close[i]

I just want to put a "*" at the OBV value in that day. However, I know this is an array, and not supported in plottext. I know how to get lastvalue, beginvalue. But I want the value of that position, just like C[i], but i fill OBV(i), error!
expert, please help

for( i = 0; i < BarCount; i++ )
{
if( Buy[i] ) PlotText( "*", i, OBV(), colorGreen);
}