Visual studio 2010 inexplicable C2146 error

"C" does not have "bool", "true" or "false".

"C++" does have them (as does "C#") as recognizable data types.

The Visual Studio IDE editor highlights "bool", "true", and "false" in blue because it does recognize them as language keywords and even does that in files with the ".C" file type, even though the compiler will complain (this is a bug in the IDE in my opinion).

Microsoft defined "BOOL", "TRUE", and "FALSE" in one of their ".H" files and most of the windows APIs, MFC APIs, etc all return things of those types. However, those types are nothing more than "int" or specific values of "int". Because of this, you will often see a mix of "bool" (lower case) and "BOOL" uppercase in "C++" programs. I try to keep the uses apart, only using "BOOL" when dealing with API returned values or API parameters.

Your code compiles just fine (VS 2008, 2010) provided #include <windows.h> is used.

"Is there some compile option that forces all data to be declared ahead of code?" — there is not such rule; there is a requirement to declare all variables before they are used. It's irrelevant as you don't use the variable off.

Perhaps you need to show more of your code.

—SA

In the first version your declaration of y comes within a block of dead code! All execution paths before that return from main, so everything below the if statement will never be executed.

Solution: Don't use premature return statements. It is a bad practice anyhow. Instead use a variable to hold the return value, and execute the remainder of the code dependend on that value, e. g. like this:

int main() {
   BOOL x;
   int result = 0; // return value - initialized to 'ok'
   if (x)
      result = 1;
   else
      result = 2;

   if (result == 0) {
      BOOL y;
      y = FALSE;
   }
   return result;
}

Note that while the declaration of y is still semantically dead code (i. e. the semantics of your code prevent it from being executed), the compiler will no longer complain, because syntactically the code is still 'alive'.

P.S.: I just wondered why this would produce an error - it should at worst produce a warning. The error you got is quite probably caused by something different. After looking at your posting again, I noticed that you mentioned having included windows.h only in the second version - and as others have pointed out you'd need that for the definition of the symbols of BOOL and FALSE.

Sorry for bothering you with a solution to a problem you hadn't asked about ;)