asp.net
<h1>' (single quote)</h1>
The single quote character (') introduces a comment line in VB.NET code. It can be used anywhere on a source line. The end of the physical line ends the comment.
<h1>Rem</h1>
The keyword Rem also introduces a comment in VB.NET code. It can be used anywhere on a source line. The end of the physical line ends the comment.
<h1>/* and */ </h1>
The characters /* and */ open and close respectively a multi-line comment block--the so called regular comment--in C# code. Regular comments can span over a section of a line, a single line, or multiple lines.
<h1>//</h1>
The double slash characters (//) introduce a one-line comment in C# code and can be placed anywhere on a source line. The one-line comment extends to the end of the line. Equivalent to ' and Rem in VB.NET.
<h1>///</h1>
The comments introduced by tripple slash characters (///) are a C#-specific feature. By means of XML markup you can document your code (e.g. <param> is used for describing parameters). If you run the compiler with the /doc option, it automatically generates an XML documentation file.
<h1><!-- and --> </h1>
The characters <!-- and --> are standard HTML (adopted from SGML) comment delimiters. Note, that the comment text is sent to the browser and thus visible outside (source code).
<h1><%-- and --%></h1>
Server-Side Comments (<%-- --%>) enable ASP.NET page developers to prevent server code (including server controls) and static content from executing/rendering. They assume a similar role to the standard HTML comments with the smashing difference that the text of the comment is not sent to the browser.