a in aGlobal() is 3 (the global)
a in main() is 13, global ::a is 3
a in passByValue() is 26
a in main() after passByValue() is 13
*a in passByPointer() is 26
a in main() after passByPointer() is 26
add(13, 3) = 16
countCalls() has now been called 3 times
