C++ is very case sensitive. A #include and #Include Are not the same thing. In fact, #Include does not exist at all. So whether you are creating your own function or using one from a library, check for case sensitivity.
A few typo's there, but pretty much everything is case-sensitive.
A couple of notes:
1. Generally preprocessor definitions/macros are all upper-case. That's only by convention.
2. Preprocessor commands (#ifndef, define, endif, include) are all lower-case.
3. When you #include a file, or open a file, the case-sensitivity depends on your OS. On windows, filenames are not case-sensitive, on linux, they are case-sensitive. I always match the proper case for my files to guarantee portability, even if I'm on windows.