There is no clear source of truth for C. Depending on what you want to do there is quite different approaches. C for embedded systems tends to look quite different from C for systems programming. For instance MISRA is a C coding standard for embedded devices in Motor Vehicles (but many of its ideas are ideas from writing robust embedded systems), it says don't use things like dynamic memory. You'd never use that if you are writing software for linux/windows. So learning C "properly" would be about learning the different approaches people use in C to write robust code and what tradeoffs they are making. Understanding the C standard and the variations. Understanding bare metal programming. Understanding the effect of different underlying processors and hardware architectures. Understanding systems programming and how to consume APIs and how to create reusable binary modules. Understanding the compiler/build system the intermediate files / code generation / memory layout. Read a variety of books ( including K&R ) and study code ( Luas implementation is some very nicely written C )
