What is an Identifier?
1. The case of the alphabetic character is significant. Using "INDEX" for a variable is not the same as using "index" and neither of them is the same as using "InDex" for a variable. All three refer to different variables.
2. As C is defined, up to eight significant characters can be used and will be considered significant. If more than eight are used, they may be ignored by the compiler. The HiTech C compiler used with the Applix 1616 alllows 31 significant characters, and prepends an underscore ( _ ).
It should be pointed out that some C compilers allows use of a dollar sign in an identifier name, but since it is not universal, it will not be used anywhere in this tutorial. Check your documentation to see if it is permissible for your particular compiler.