ASP.NET - gridview paging

gridview have select all(checkbox)here using paging...now i select 5 rows in first page next go second page here i select 6 rows then go to 5 page here i select 7 rows  finally i want check all rows......my problem is go to second page first page value is clear

check this,
http://www.c-sharpcorner.com/uploadfile/rohatash/gridview-paging-sample-in-asp-net/

check this,
http://www.c-sharpcorner.com/uploadfile/rohatash/gridview-paging-sample-in-asp-net/