A course takes you from 0 to basic knowledge of C, not in-depth knowledge. In-depth knowledge comes from years of experience.
Unless you have a very specific reason to have in depth knowledge of C, I am not sure it actually makes that much sense to go further than the basics before diving into "doing stuff" with the language. Most of the complexity of programming is going to come from experience, and no one really learns "everything". You carve out a piece of what's important to you.
So for example you could take this Introduction to C programming Coursera course (https://www.coursera.org/specializations/c-programming) to learn the basics.
Then, if your interested in say Arduino projects you could take this Arduino/C Programming Coursera course (https://www.coursera.org/learn/arduino-platform)
Or, if you wanted to learn more about Embedded Systems you could take this Coursera course which also uses C (https://www.coursera.org/learn/introduction-embedded-systems)
If your looking for more general knowledge like you would get in University, you could check out this book "Algorithms in C" from the library.
There are so many paths you can take, and "learning C" or "learning <enter-programming-language-here>" is the very very beginning.