To clarify, you mean C code right? C# is .Net CLR code that does not compile down to machine code.
I would suggest rather that you learn C code instead of working with assembler...it is much easier to use (once you understand it), and it all compiles down to the same thing (the .hex machine code).
There is no good direct way I know of to convert C code into assembler code, because assembler is not a 'step' in the process of compilation. There are tools to convert X86 code into assembler but these won't work, as you want to work with the registers and whatnot in your particular microprocessor. Somebody else might know something, but in general it is a rather manual process.