Comparisons

s1.compare(s2) returns an int
< 0    if s1 < s2
> 0    if s1 > s2
= 0    if s1 equal to s2
Can also use  <,  <=,  ==,  >=,  >,  !=
eg. s1 == s2
Don't do "abc" == "abc"
Will compile, but doesn't make sense
std::string("abc") == std::string("abc")