Do I have to have Main to compile my C# file?

[ajoo]

What if I just want to write some libs?

Thanks a lot!

[saucer]

no, you do not need to, but you need to specify the output target to be a library type, for example:

csc /target:library /out:TestMain.dll TestMain.cs

[ajoo]

why the result is .dll or .exe?
does that imply the result file can only be run on a specific OS?

[saucer]

theoretically, they could be run on all platforms as long as there are .NET runtime on these platforms and you did not use Windows specifics, but as you know, that may never the case

exe has a Main entry point and can be executed alone, while dll cannot

[ajoo]

when I deploy my class lib, am I deploying just a dll file? how my users compile their code which uses my class?
Java has class path so that it can find the class file, how can CLR find the dll containing my class?

for example, My user write:
class Test{
void f(){LibClass.fff();}
};
and the LibClass is in my blahblah.dll,
how can clr find out that the LibClass is actually in the "blahblah.dll"?

[saucer]

you can use switches like
/reference:SomeOtherDll.dll;SomeOtherDll2.dll /lib:ThePathToSomeOtherDll1,ThePathToSomeOtherDll2

you can also add these options in csc.rsp located in C:\WINNT\Microsoft.NET\Framework\v1.0.3705\csc.rsp
which C# compiler reads automatically