HOW: compile C# in command prompt

Hi,

I am try to compile my source code through command prompt. The source code is place in "My Document" directory and the csc.exe is place in "windows\xxx" directory (the path is very long, I use xxx to represent the path). While I am still in "My Document" directory and try to send the simple command like this:

csc /?

it was failed because it couldn recognise the csc as a command. But when I change the directory into "windows\xxx", it is working. May I know what should I do so that I can compile the C# source code in "My Document" directory?

THank YOu @!