<form id="form1" runat="server">
<asp:Button ID="Button1"
runat="server"
onclick="Button1_Click"
Text="Click"
Width="74px" BackColor="#FF6666" />
<div style="width: 93px">
<asp:Label ID="Label1"
runat="server"
Text="Label" BackColor="Yellow" ForeColor="Black"></asp:Label>
</div>
</form>
<asp:Button ID="Button1"
runat="server"
onclick="Button1_Click"
Text="Click"
Width="74px" BackColor="#FF6666" />
<div style="width: 93px">
<asp:Label ID="Label1"
runat="server"
Text="Label" BackColor="Yellow" ForeColor="Black"></asp:Label>
</div>
</form>
Code Behind
protected void Button1_Click(object sender, System.EventArgs e)
{
StringBuilder stringA = new StringBuilder();
stringA.Append("those are text. ");
StringBuilder stringA2 = new StringBuilder(" another text.");
stringA.Append(stringA2);
Label1.Text = stringA.ToString();
}