First, algostuff.hpp includes all header files that may be necessary to implement the examples,
so the program doesn’t have to do it. Second, it defines three auxiliary functions:2
1. INSERT_ELEMENTS() inserts elements into the container that is passed as the first argument.
These elements get the values from the value passed as the second argument up to the value
passed as the third argument. Both argument values are included, so this is not a half-open range.
2. PRINT_ELEMENTS() prints all elements of the container that is passed as the first argument,
separated by spaces. You can pass a second argument optionally for a string that is used as a
prefix in front of the elements (see Section 6.6, page 216).
3. PRINT_MAPPED_ELEMENTS() is the same for containers with a key/value pair: map, multimap,
unordered map, and unordered multimap