Remove airthmetic prefix from a negative integer in C# .Net

You have to use Math.Abs for this. Here i am adding, subtracting and multiplying the two numbers. In Third TextBox i am passing the Operator +,-,*, /. If any others operator is provided then it will give the error.

HTML:

<form id="form1" runat="server">
    <div>
        X:<asp:TextBox ID="txtXvalue" runat="server" /><br />
        Y:<asp:TextBox ID="txtYvalue" runat="server" /><br />
        <asp:TextBox ID="txtOp" runat="server" MaxLength="1" />
        <asp:Button Text="Calculate" OnClick="Calculate" runat="server" />
        <asp:Label ID="lblResult" runat="server" />
    </div>
    </form>

C#:

protected void Calculate(object sender, EventArgs e)
        {
            int x = int.Parse(this.txtXvalue.Text.Trim());
            int y = int.Parse(this.txtYvalue.Text.Trim());
            float z = 0;
            string op = this.txtOp.Text.Trim();
            switch (op)
            {
                case "+":
                    z = x + y;
                    this.lblResult.Text = (Math.Abs(z)).ToString();
                    break;
                case "-":
                    z = x - y;
                    this.lblResult.Text = (Math.Abs(z)).ToString();
                    break;
                case "*":
                    z = x * y;
                    this.lblResult.Text = (Math.Abs(z)).ToString();
                    break;
                case "/":
                    z =(float) x / y;
                    this.lblResult.Text = (Math.Abs(z)).ToString();
                    break;
                default:
                    Response.Write("Invalid Operator");
                    break;
            }

        }

Thank You.