count the no records are selected or un selected in gridview

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C#

ASP.NET

How to count number of checkboxes checked/unchecked in gridview using asp.net

i am using this code in .aspx

<asp:GridView ID="gridlob" runat="server" AutoGenerateColumns="False"
        DataSourceID="SqlDataSource2" width="50%"
          onrowdatabound="gridlob_RowDataBound" >
        <Columns>
            <asp:BoundField DataField="LOUPe_LOB" HeaderText="Line Of Bussiness"
                SortExpression="LOUPe_LOB" />

               <asp:TemplateField HeaderText="Grouping">


              <ItemTemplate>
                <asp:CheckBox ID="chkReimbursable" runat="server" />
                </ItemTemplate>
                </asp:TemplateField>

        </Columns>
    </asp:GridView>

and i write code in code behind like this

DataRowView drview = e.Row.DataItem as DataRowView;
if (e.Row.RowType == DataControlRowType.DataRow)
{

    CheckBox check = (CheckBox)e.Row.FindControl("chkReimbursable");
    
        if (drview[1].ToString() == "Y")
        {
            check.Checked = true;
            

        }

      else {
            check.Checked = false;

            
        
        }

My requirement if user have a chance to maximum 19 records after selecting 19 records he is trying to select another record the remaining checkboxes are disabled. and user select the checkbox each and every time count the no of records are selected and no of records are unselected