| cppreference.com -> Pre-processor commands |
| #, ## | manupilate strings |
| #define | define variables |
| #error | display an error message |
| #if, #ifdef, #ifndef, #else, #elif, #endif | conditional operators |
| #include | insert the contents of another file |
| #line | set line and file information |
| #pragma | implementation specific command |
| #undef | undefine variables |
| Predefined variables | miscellaneous variables |