Value and Reference Parameters

• Review how to create functions
• Local and Global Scope Rules
  • A variable exists from its declaration to the end of its enclosing block
  • Variables declared without any block have global scope
    • Global variables can be referenced in other source files (demonstrate with example)
  • Variables can be "hidden" by declaring another variable of the same name
  • A hidden global variable can be referenced using the scope resolution operator:  ::
• Parameter Types
  • Value parameters
    • Semantics:  The formal parameter gets the value of the actual parameter (as in an assignment).
    • Example:
      • Suppose we have the function void print(string s) { cout << s << endl; } which we call as print("Hello, World"); within our program.
      • It's as though there is an assignment statement:  s = "Hello, World"; as the first statement in the function.
    • Value parameters DO NOT change in the calling function
      • Example:  value_parms.cpp
  • Reference Parameters
    • Semantics:  Rather than passing the value of the actual parameter, we pass the location (aka address)  of the parameter, so the called function knows how to modify the parameter directly
    • Example:
      • Suppose we have the function void print(int &x) { cout << x << endl; } which we call as print(var); within our program.
      • The "&" before the x means that the function print is expecting an address, not a value.
    • Actual reference parameter arguments MUST be variables (i.e., they cannot be literals)
    • Reference parameters MAY have there values changed by the called function.
    • Array are automatically passed by reference
    • Example:  reference_parms.cpp