Swapping TextBox Value using Button in ASP.NET

Refer this code

<div>
    <asp:TextBox ID="txtTextbox0" runat="server" Text="1" />
    <asp:Button ID="btnButton0" runat="server" Text="btnButton0" OnClick="btnButton_Click" />
    <br />
    <asp:TextBox ID="txtTextbox1" runat="server" Text="2" />
    <asp:Button ID="btnButton1" runat="server" Text="btnButton1" OnClick="btnButton_Click" />
    <br />
    <asp:TextBox ID="txtTextbox2" runat="server" Text="3" />
    <asp:Button ID="btnButton2" runat="server" Text="btnButton2" OnClick="btnButton_Click" />
    <br />
    <asp:TextBox ID="txtTextbox3" runat="server" Text="4" />
    <asp:Button ID="btnButton3" runat="server" Text="btnButton3" OnClick="btnButton_Click" />
    <br />
    <asp:TextBox ID="txtTextbox4" runat="server" Text="5" />
    <asp:Button ID="btnButton4" runat="server" Text="btnButton4" OnClick="btnButton_Click" />
</div>

C#

protected void btnButton_Click(object sender, EventArgs e)
{
    string number = string.Empty;
    if (ViewState["Number"] == null)
    {
        ViewState["Number"] = 0;
    }

    switch (ViewState["Number"].ToString())
    {
        case "0":
            number = this.txtTextbox0.Text;
            this.txtTextbox0.Text = this.txtTextbox1.Text;
            this.txtTextbox1.Text = number;
            break;
        case "1":
            this.txtTextbox0.Text = "3";
            number = this.txtTextbox1.Text;
            this.txtTextbox1.Text = (Convert.ToInt32(this.txtTextbox2.Text) - 1).ToString();
            this.txtTextbox2.Text = number;
            break;
        case "2":

            number = this.txtTextbox2.Text;
            this.txtTextbox2.Text = this.txtTextbox3.Text;
            this.txtTextbox3.Text = number;
            break;
        case "3":
            number = this.txtTextbox3.Text;
            this.txtTextbox3.Text = this.txtTextbox4.Text;
            this.txtTextbox4.Text = number;
            break;
    }

    ViewState["Number"] = Convert.ToInt32(ViewState["Number"]) + 1;
}