Comments by YassineYousfi (Top 3 by date)

You are having issues in understanding basic programming stuff.
example:
dgv.Columns.Add() : u should pass something to the Add function, ask yourself the question "Add what" Add(<what here="">).
dgv.Columns.Count = (Dt.Rows.Count + 2) : you cannot change that property it's readonly, the only way to change a readonly property is by adding/removing items from dvg.Columns.

debug the exact line that throws the error. and tell which object that crushes.