Due to the processes c# goes through when it is executed it is impossibble to run code without a class, a class is what is executed and called upon when the program is running. without it there is no program.
however you might be talking about making a program without a class library project, if you are then you can write a program without using a library, you could throw every part of the code in behind a form and its buttons, however, it is bad practice to do so, it is messy, and harder to debug and change, it also means the code is no longer re-useable.
so to cover
-Can i not have classes?
No, you have to have atleast 1
-Can i ignore class libraries?
Yes but its bad to do so
Rhys Whymark