body>
    form id="form1" runat="server">
    div>

        姓名：asp:TextBox ID="txtUser" runat="server">/asp:TextBox>
        br />
        br />
        性别：asp:RadioButtonList ID="rblsex" runat="server">
            asp:ListItem>男/asp:ListItem>
            asp:ListItem>女/asp:ListItem>
        /asp:RadioButtonList>
        密码：asp:TextBox ID="txtPwd" runat="server" TextMode="Password">/asp:TextBox>
        br />
        移动电话：asp:TextBox ID="txttel" runat="server"
            ontextchanged="TextBox3_TextChanged">/asp:TextBox>
        br />
        简介：br />
        asp:TextBox ID="txtinfo" runat="server">/asp:TextBox>
        br />
        br />
        asp:ImageButton ID="ImageButton1" runat="server" Height="58px"
            ImageUrl="~/img/QQ截图20130909140346.png" Width="72px" />
        br />
        br />
        br />
        br />
        br />

    /div>
    /form>
/body>

protected void txtNum2_TextChanged(object sender, EventArgs e)
    {
        if (txtNum2.Text.Length == 0)
        {
            //Page.RegisterClientScriptBlock("","script>alert('请输入一个数');/script>");
            Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "", "script>alert('请输入一个数');/script>");
            txtNum2.Focus();
        }
        else
        {
            int result;
            bool n1 = Information.IsNumeric(txtNum2.Text.Trim());
            if (n1)
            {
                result = int.Parse(txtNum2.Text.Trim()) % 2;
                if (result == 0)
                {
                    txtSum.Text = "偶数";
                }
                else
                {
                    txtSum.Text = "奇数";
                }
            }
        }
    }
}