Correct C

A monster list about bad code practices for the absolute beginners. Things obviously should be taken with a grain of salt, just stating the obvious.

Functions without parameters will be defined with void in the parameter list, as opposed to leaving it empty. (e.i. (void) rather than ())
(public-facing) names mustn't be prefixed with _, this is a reserved identifier.
typedefs mustn't be suffixed with _t, this is a POSIX reserved identifier.
typedefs are discouraged, unless the name alias is clear in what it stores. (e.i. u32 for a 32 bit unsigned integer)
Functions should do one thing, and do it well.
inline functions should serve as a replacement for macro definitions, don't put things in here that you wouldn't put in a macro. (block ≤5 lines)
Mark all implementations in a *.c file with static if there isn't a matching definition in a *.h file. (unless there's a clear reason to)
When a function parameter takes in a pointer, and does not modify the pointed at data, a const pointer should be used. (const int *ptr)
Try to limit yourself at ~112 columns, but generally avoid overly long lines.