Clear (Empty) DataTable rows on Button Click using C# in ASP.Net

how to empty the datatable

I want to empty the datatable(addtogv) of data for the new input process

i have this codes in c# 

DataTable addtogv = new DataTable();
if (!Page.IsPostBack)
{
    if (ViewState["records"] == null)
    {
        addtogv.Columns.Add("item_no");
        addtogv.Columns.Add("item_name");
        addtogv.Columns.Add("qun");
        ViewState["records"] = addtogv;

addtogv = (DataTable)ViewState["records"];
addtogv.Rows.Add(DropDownList3.SelectedItem.Value, DropDownList3.SelectedItem.Text, txtqnt.Text);
GridView1.DataSource = addtogv;
GridView1.DataBind();