Appendix A provides a concise summary of the basic elements of the Objective-C language. Its scope is the Objective-C language extensions to ANSI C. The fundamental elements of the C programming language are not covered here; they can be found in numerous other references.
The lexical rules for variable names in Objective-C are identical to those for ANSI C—a variable is defined with a letter or underscore, followed by any combination of letters, underscores, and the digits 0–9. Uppercase and lowercase letters are distinct.
Objective-C Reserved Words
In a programming language, a reserved word is a symbol that has a special meaning in the language, and hence should not be used as a variable name. Objective-C ...