You’ve learned quite a bit! You now know a bit about how scope works for functions and files, as well as how to make functions more flexible for different use cases:

• Scope is the region of code that has access to an element.
  • Globally scoped variables are accessible everywhere.
  • A variable created inside a function has local scope and can’t be accessed outside the function.
• C++ functions are usually split to make code more modular:
  • The declaration in a header file.
  • The definition in another .cpp file.
• Programs with multiple .cpp files need to be linked at compile time:

  g++ main.cpp fns.cpp

• Header files must be included in the file with main():

  #include "fns.hpp"

• You can define a function inline using the inline keyword, which may or may not improve execution speed.
• Default arguments can be added to function declarations so that you can call the function without including those arguments.
• You can overload C++ functions so that they handle different types of input and return different types.
• A function template enables a function to behave the same with different types of parameters.