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);
}
Note that the constant integer x is defined as 400 before it is used in the library.h print function.
For functions defining before use means that you must have the entirety of your function above wherever it is called, like this:
void foo(const string greeting)
{
print(greeting);
newline();
}
void bar()
{
foo("Good news, everyone!");
}
Note that when the function foo that is called in the function bar it is defined above the function bar.