### Reserved Keywords

Keywords are identifiers reserved by the language for special use. You can use them for preprocessor macro names but that is, however, considered poor programming style.

Only the exact character case and spelling of keywords is reserved. For example, auto is reserved, but AUTO is not.

Keywords reserved by the C programming language are:

`auto` | `break``` | `case``` | `char`
`const` | `continue` | `default` | `do`
`double` | `else``` | `enum` | `extern`
`float` | `for``` | `goto``` | `if```
`int` | `long` | `register` | `return`
`short` | `signed` | `sizeof` | `static`
`struct` | `switch``` | `typedef` | `union`
`unsigned` | `void` | `volatile` | `while`

Identifier names should not start with an underscore (_) followed by an uppercase letter, and should not contain two underscores (__) anywhere. The compiler and library use identifiers beginning with single and double underscores for their own purposes.

Keywords
Keywords in C and C++
Additional IBM C and C++ Compilers Predefined Macros
ISO/ANSI Standard Predefined Macro Names