compiling C# program using vs2012 command prompt

Question

how to compile a C# program using vs2012 command prompt ?

i wanted to compile my program(Prog name:Demo.cs) which is in this folder(C:\Pra)

when i am trying to compiling my prog like this

C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC>C:\Pra>csc Demo.cs

i am getting an error i.e Acess is denied

HOW CAN I SOLVE THIS,Please help me.

Thank you