Functions and references

A function has a return type and typed parameters, and it must be declared before it is called. By default, arguments are copied (pass by value), so a function that changes its parameter changes only its own copy. Use pass by reference, as in void addBonus(int& score), when the function should change the caller's variable.

Use a const reference, as in const std::vector<int>& v, to read a large object without copying it. That second form is how you pass strings and containers almost everywhere. A reference is simply another name for an object that already exists, and it must be tied to that object when it is created.

Never return a reference to a local variable, because the local is destroyed when the function returns.