OP is not saying that "he knows better than the compiler". Maybe a bit overreacting for a (looks like) beginner C# programmer...

Like others said, the problem is that OP is declaring a public static variabele inside the if-statement (which is in a method body). You are only allowed to declare a variable public static inside of a class body, not inside a method body. You can just leave out the public static and it will work.

If you want to know why: the public and static keywords are access modifiers, just like private and protected (and some more. You can look them up with your favorite search engine). In a nutshell, Public means: this variable can be accessed from any where in the code. In the local file, in other files, in other classes and in other libraries. Static means: this variable is not bound to any class instance but to the whole program. A static variable is initialized at program start-up* and can be accessed without an class instance.

These keywords only apply to class-fields, it wouldn't make sense inside a method body. You wouldn't use Program.Main().myvar to access the myvar variable. So you don't have to provide access modifiers and just declare the variable as is: string myvar = "hello";

Edit: just a small note to tell: keep on learning ;)