seprating numbers in grid view

you will write 1905 to cell and it becomes automaticly 1,905 while you are writing..is this you want?

you can get digit count like in this link http://www.dotnetperls.com/integer-digit-count
or of course there must be some other ways..
when you get the digit count you can put your comma anywhere you want example : http://csharp.net-informations.com/string/csharp-string-insert.htm
and if you do all this work inside DataGridView.CellValueChanged Event (http://msdn.microsoft.com/en-us/library/system.windows.forms.datagridview.cellvaluechanged.aspx) you can achieve , i suppose