Why challenges codes can not run on code playground ?

Question

It is the very good way to learn more about a language

Answer 1

agree @Anibal. I do this.

Answer 2

Because most of them are snippets.
They wont run without the whole program structure
You can post the questions here if you have any doubt

Answer 3

Just a fragment

Answer 4

yes but is a good trainning complete the code to run and modify some things to make tests and learn more about especific topics