C# coding inside HTML tags

In aspx.cs:
public partial class _Default : System.Web.UI.Page
{
//Create public variable inside the class
    public string value = string.Empty;
    protected void Page_Load(object sender, EventArgs e)
    {
       }
protected void btn1_Click(object sender, EventArgs e)
    {
//set the variable value on button click
        value="test";
    }
}

In aspx page
//Create a label and get the variable value
 <%=value %>
//Button on which click set the value



Same thing u can do for complete ur requirement