Calculate total for each row in gridview

Here's a sample for you

GridView

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:BoundField DataField="Item" HeaderText="Item" />
            <asp:BoundField DataField="Price" HeaderText="Price"/>
            <asp:TemplateField HeaderText="Quantity">
                <ItemTemplate>
                    <asp:TextBox ID="txtQuantity" runat="server" OnTextChanged = "Quantity_Changed" AutoPostBack = "true"></asp:TextBox>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Total">
                <ItemTemplate>
                    <asp:Label ID="lblTotal" runat="server" Text="0"></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>

Code

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DataTable dt = new DataTable();
            dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Item"), new DataColumn("Price"), new DataColumn("Total") });
            dt.Rows.Add("Shirt", 200, 0);
            dt.Rows.Add("Football", 30, 0);
            dt.Rows.Add("Bat", 22.5, 0);
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
    }

    protected void Quantity_Changed(object sender, EventArgs e)
    {
        TextBox txtQuantity = (sender as TextBox);
        GridViewRow row = (txtQuantity.NamingContainer as GridViewRow);
        Label lblTotal = (row.FindControl("lblTotal") as Label);
        lblTotal.Text = (int.Parse(txtQuantity.Text) * int.Parse(row.Cells[1].Text)).ToString();
    }