The binary arithmetic assignment operators: +=, -=, /=, *= and %= are extendible as well. While some of these operators would not be meaningful on the Date class, at least the first four would each be meaningful on the Complex class.
Defining these operators on the Complex class will permit the following:
aComplex += bComplex; aComplex -= bComplex; aComplex /= bComplex; aComplex *= bComplex;
When appropriate, these binary assignment operators could be defined on any class. For example: cmlxasgn.cpp.