I added checkbox in my webpage using:

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

But then my calculation of price*quantity having error where it display the total in another column and row.

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script type="text/javascript">  

        function CalculateTotals() {  
            var gv = document.getElementById("<%= GridView1.ClientID %>");  
            var tb = gv.getElementsByTagName("input");  
            var lb = gv.getElementsByTagName("span");

            var sub = 0;  
            var total = 0;  
            var indexQ = 1;  
            var indexP = 0;  
            var price = 0;  

            for (var i = 0; i < tb.length; i++) {  
                if (tb[i].type == "text") {  
                    ValidateNumber(tb[i]);  

                    price = lb[indexP].innerHTML.replace("$", "").replace(",", "");  
                    sub = parseFloat(price) * parseFloat(tb[i].value);  
                    if (isNaN(sub)) {  
                        lb[i + indexQ].innerHTML = "0.00";  
                        sub = 0;  
                    }  
                    else {  
                        lb[i + indexQ].innerHTML = FormatToMoney(sub, "$", ",", "."); ;  
                    }  

                    indexQ++;  
                    indexP = indexP + 2;  

                    total += parseFloat(sub);  
                }  
            }  

            lb[lb.length - 1].innerHTML = FormatToMoney(total, "$", ",", ".");  
        }  

        function ValidateNumber(o) {  
            if (o.value.length > 0) {  
                o.value = o.value.replace(/[^\d]+/g, ''); //Allow only whole numbers  
            }  
        }  
        function isThousands(position) {  
            if (Math.floor(position / 3) * 3 == position) return true;  
            return false;  
        };  

        function FormatToMoney(theNumber, theCurrency, theThousands, theDecimal) {  
            var theDecimalDigits = Math.round((theNumber * 100) - (Math.floor(theNumber) * 100));  
            theDecimalDigits = "" + (theDecimalDigits + "0").substring(0, 2);  
            theNumber = "" + Math.floor(theNumber);  
            var theOutput = theCurrency;  
            for (x = 0; x < theNumber.length; x++) {  
                theOutput += theNumber.substring(x, x + 1);  
                if (isThousands(theNumber.length - x - 1) && (theNumber.length - x - 1 != 0)) {  
                    theOutput += theThousands;  
                };  
            };  
            theOutput += theDecimal + theDecimalDigits;  
            return theOutput;  
        }

        function Validate(sender, args) {
            var gv = document.getElementById("<%= GridView1.ClientID %>");
            var checkBoxes = gv.getElementsByTagName("input");
            for (var i = 0; i < checkBoxes.length; i++) {
                if (checkBoxes[i].type == "checkbox" && checkBoxes[i].checked) {
                    args.IsValid = true;
                    return;
                }
            }
            args.IsValid = false;
        }
    </script>  
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <asp:gridview ID="GridView1"  runat="server"  ShowFooter="true" AutoGenerateColumns="false">  
        <Columns>  

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

        <asp:BoundField DataField="RowNumber" HeaderText="Row Number" />  
        <asp:BoundField DataField="Description" HeaderText="Item Description" />  
        <asp:TemplateField HeaderText="Item Price">  
            <ItemTemplate>  
                <asp:Label ID="LBLPrice" runat="server" Text='<%# Eval("Price","{0:C}") %>'></asp:Label>  
            </ItemTemplate>  
            <FooterTemplate>  
                <b>Total Qty:</b>  
            </FooterTemplate>  
        </asp:TemplateField>  
        <asp:TemplateField HeaderText="Quantity">  
            <ItemTemplate>  
                <asp:TextBox ID="TXTQty" runat="server" onkeyup="CalculateTotals();"></asp:TextBox>  
            </ItemTemplate>  
            <FooterTemplate>  
                <asp:Label ID="LBLQtyTotal" runat="server" Font-Bold="true" ForeColor="Blue" Text="0" ></asp:Label>       
                <b>Total Amount:</b>  
            </FooterTemplate>  
        </asp:TemplateField>  
        <asp:TemplateField HeaderText="Sub-Total">
            <ItemTemplate>  
                <asp:Label ID="LBLSubTotal" runat="server" ForeColor="Green" Text="0.00"></asp:Label>  
            </ItemTemplate>  
            <FooterTemplate>  
                <asp:Label ID="LBLTotal" runat="server" ForeColor="Green" Font-Bold="true" Text="0.00"></asp:Label>  
            </FooterTemplate>  
        </asp:TemplateField>  
        </Columns>  
    </asp:gridview>  
        </div>
    </form>
</body>
</html>

For my code behind:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

namespace SystemTesting
{
    public partial class product : System.Web.UI.Page
    {
        private void BindDummyDataToGrid()
        {

            DataTable dt = new DataTable();
            DataRow dr = null;

            dt.Columns.Add(new DataColumn("No"));
            dt.Columns.Add(new DataColumn("RowNumber", typeof(string)));
            dt.Columns.Add(new DataColumn("Description", typeof(string)));
            dt.Columns.Add(new DataColumn("Price", typeof(string)));

            dr = dt.NewRow();
            dr["No"] = "";
            dr["RowNumber"] = 1;
            dr["Description"] = "Nike";
            dr["Price"] = "1000";
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr["No"] = "";
            dr["RowNumber"] = 2;
            dr["Description"] = "Converse";
            dr["Price"] = "800";
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr["No"] = "";
            dr["RowNumber"] = 3;
            dr["Description"] = "Adidas";
            dr["Price"] = "500";
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr["No"] = "";
            dr["RowNumber"] = 4;
            dr["Description"] = "Reebok";
            dr["Price"] = "750";
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr["No"] = "";
            dr["RowNumber"] = 5;
            dr["Description"] = "Vans";
            dr["Price"] = "1100";
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr["No"] = "";
            dr["RowNumber"] = 6;
            dr["Description"] = "Fila";
            dr["Price"] = "200";
            dt.Rows.Add(dr);
            //Bind the GridView  
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindDummyDataToGrid();
            }
        }
    }
}

Because you added the checkbox, your arrays tb and lb might have gotten longer by 1. That may cause your offset issue.

commented: Then how should I fix it? +0
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