Here are three alternative implementations of a 2d dynamic array class. Each
uses one of the ideas discussed today in class (allocating each row
independently, allocating a big chunk of space, re-using the MyArray class).
Observe that their interface is (almost) identical and they only differ in
their internal workings. As a result, a program written for one can be compiled
to use the other without any changes (to prove this point, I'm using the same
test program for all three). This is generally a good idea...

Study these programs and let me know if you have questions or comments!