I ran into a compilation issue.
This link explains the problem well: https://stackoverflow.com/a/5499222/3736700
For example, in a header file, it is generally not considered a good idea to put the line using namespace std; (or to use any namespace, for that matter) because it can cause names in files that include that header to become ambiguous. In this setup, you would just #include <string> in the header, then use std::string to refer to the string type.
