Preprocessors
| #include | Insert a source file. | 
| #define | Define a preprocessor
constant. | 
| #if | Branch based on an expression. | 
| #ifdef | Branch if preprocessor constant has been defined? | 
| #ifndef | Branch is a preprocessor
constant has NOT been defined. | 
| #line | Specify the number of the next source line. | 
| #undef | Remove a preprocessor constant. | 
| #pragma | Perform an implementation dependent action??? | 
| #else | Executed if #if
#ifdef or #ifndef fails. | 
| #error | Write an error message. | 
| #elif | Executed when an #if fails. | 
| #endif | Close #if #ifdef or
#ifndef |