How to echo something in C# in an .aspx file

Question

I know you can do this

<%= Request.Form[0] %>

But how do you do something like this?

<% if(Request.Form[0]!=null)
     echo "abc";
%>

Answer 1

<% if(Request.Form[0]!=null)
    Response.Write("abc");
%>

Answer 2

Maybe you want to show the form value unless it doesn't exist then show "abc"?

<%= Request.Form[0] ?? "abc" %>

Or you could can use if blocks and normal markup inside.

<% if(Request.Form[0]!=null) { %>

   <div class="echo">abc</div>

<% } %>