Why didn't she use puts? She instead uses printf incorrectly. Some of the things she says seem to be a bit wrong, for example "it is possible to access memory outside of the defined-size of the array", no it is not, this is undefined behaviour.
"it is important to also initalise it on the same time" So you will get bugs with the same behaviour that are difficult to detect instead of the compiler warning you or bugs with different behaviour each time? It reminds me when people do try{code}catch{} just to avoid crashes without avoiding what causes them.
"possibly a valid address in memory or maybe an invalid one, which would cause undefined behavior" False, it is always valid.
This is a bad video, in fact, why is it even a video? Why isn't it a simple webpage? It would make our life easier that way. Not to mention that she is using a terrible, non-free editor to begin with.
Please, avoid posting low quality stuff such as this, thanks.