I am not sure on executin an app within .net on a server, but pretty sure this can be done as it was possible in classic asp with the use of a component.

As the C compiler is commandline, I can see no reason why this could not be executed. You will need to output your code from the asp page to a file, execute the commandline compiler (directed at the outputted file), and then return the result to a string, etc. I am pretty sure you can compile in a test mode or do a test compile? Problems arrise when using various switches for the compiler and also the compile order when one compiled code relys on another piece of compiled code, headers, libs, etc.

Not to sure on the security issues here, but would imagine there could be some dangerous results, even with a test compile, such as the compiler crashing!

I would imagine this is very possible, but probably not advisable. I dont think you would find an ISP prepared to host it, unless you did this yourself.

Hope this is some sort of help..