What this means is that your compiler (Visual Studio) cannot find the definition for a function or variable/constant that you are trying to use. Why does this happen? Well, in order to use anything that is not a part of library.h you must first define it in your program.
For a variable
or constant, that means defining it before it is used like this:
void foo() { const int x = 400; print(x); }
void foo(const string greeting) { print(greeting); newline(); } void bar() { foo("Good news, everyone!"); }