Update ex7_22.h
Update ex7_22.h

While the original (using 'struct') was technically correct, I believe using 'class' makes more sense here.  Here's what the book states: 
"As a matter of programming style, when we define a class intending for all of its
members to be public, we use struct. If we intend to have private members,
then we use class."
andersy005/Cpp-Primer,Mooophy/Cpp-Primer,andersy005/Cpp-Primer,Mooophy/Cpp-Primer