How to increment identity in sql server 2008?

void Id()
       {
           string query = "select * from POS1 where Warehouse='" + Warehouse.Text + "' order by No";
           DataTable dt = conn.fill(query);
           string id = ""; int ID = 0;
           if (dt.Rows.Count > 0)
           {
               int ctr = dt.Rows.Count - 1;
               id = dt.Rows[ctr]["NO"].ToString();
               ID = int.Parse(id);
               ID++;
               string no =V3W000.ToUpper();
               id = no + "/" + ID;
           }
           else
           {
               string no = V3W000.ToUpper();
               ID = 1;
               id = no+ "/" + ID;
           }
           TextBox.Text = id;

   }