Merge pull request #1 from Cu3PO42/master

Add average progression.
Added 3 Assignments CH12, CH13, CH15

CH12 was about dynamic memory allocation

CH13 was about Class inheretence

CH15 was about The string Class and the Standard Template Library
New CH12 Program

Hopefully. This is about memory allocation. If not, then it's fine. If
you could add something to this one, I'd appreciate it :)
Did CH13 and CH15.