Insert to gridview by using session

You can try this
aspx:

Enter Eno<asp:textbox id="TextBox1" runat="server" asp:button id="Button1" runat="server" text="Added to grid" onclick="Button1_Click" /> 

aspx.cs

protected void Page_Load(object sender, EventArgs e)
{
    lblmsg.Text = "";
    
    if (!Page.IsPostBack)
    {
        dt.Columns.Add("eno");

 Session["reptable"] = dt;
        GridData();        
    }
}
//Load grid data from session
void GridData()
{
    GridView1.DataSource = (DataTable)Session["reptable"];
    GridView1.DataBind();
}

Add each row in the session when user add new details in the submit button

protected void Button1_Click(object sender, EventArgs e)
{
    dt = (DataTable)Session["reptable"];
    dr = dt.NewRow();
    dr["eno"] = TextBox1.Text;
dt.Rows.Add(dr);
    Session.Remove("reptable");
    Session["reptable"] = dt;
    GridData();
    TextBox1.Text = "";
}

Hope this will help you.