Hello geetasks,

Try with this, I hope this will help you.

<div>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script type="text/javascript">
        function AddRow() {
            var operator = $("[id*=txtoperator]").val();
            var value1 = $("[id*= txtvalue1]").val();
            var value2 = $("[id*= txtvalue2]").val();
            var total = $("[id*= txttotal]").val();
            if (operator != "" && value1 != "" && value2 != "" && total != "") {
                var gridRows = $("[id *= data_gridview] tr")
                var isExist = false;
                gridRows.each(function () {
                    if ($("td:nth-child(1)", $(this)).html() == operator && $("td:nth-child(2)", $(this)).html() == value1 && $("td:nth-child(3)", $(this)).html() == value2 && $("td:nth-child(4)", $(this)).html() == total) {
                        isExist = true;
                    }
                });
                if (!isExist) {
                    row = $("[id*=data_gridview] tr:last-child").clone(true);
                    $("td:nth-child(1)", row).html(operator);
                    $("td:nth-child(2)", row).html(value1);
                    $("td:nth-child(3)", row).html(value2);
                    $("td:nth-child(4)", row).html(total)
                    $("[id*=data_gridview] tbody tr:first").after(row);
                    $("[id*=txtoperator]").val('');
                    $("[id*= txtvalue1]").val('');
                    $("[id*= txtvalue2]").val('');
                    $("[id*= txttotal]").val('');
                } else {
                    alert("The Value already Exist ");
                }
            }
            return false;
        };        
    </script>
    <asp:TextBox ID="txtoperator" runat="server" class="myclass" Height="16px" Width="50px"
        MaxLength="5"></asp:TextBox>
    <asp:TextBox ID="txtvalue1" runat="server" class="myclass" Height="16px" Width="50px"
        MaxLength="5"></asp:TextBox>
    <asp:TextBox ID="txtvalue2" runat="server" class="myclass" Height="16px" Width="50px"
        MaxLength="5"></asp:TextBox>
    <asp:TextBox ID="txttotal" runat="server" class="myclass" Height="16px" Width="50px"
        MaxLength="5"></asp:TextBox>
    <br />
    <br />
    <asp:Button ID="btnAddRow" Text="Add Row" runat="server" OnClientClick="return AddRow();" />
    <asp:GridView ID="data_gridview" runat="server" />
</div>

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
        {
            DataTable dt = new DataTable();
            dt.Columns.AddRange(new DataColumn[4] { new DataColumn("Opertor ",typeof(string)),
                                new DataColumn("Value1", typeof(string)),
                                new DataColumn("Value2", typeof(string)),
                                new DataColumn("Result", typeof(string))});
            dt.Rows.Add("", "", "", "");
            data_gridview.DataSource = dt;
            data_gridview.DataBind();
        }
}

Thank you.