Functions:  Review and Parameter Types

• Function Basics
  • Functions are named, parameterized blocks of code (see former lesson's notes)
    • Example:  area.cpp and a.cpp
      • Compute the area of a rectangle:  area.cpp
        • How do we turn the area computation into a function?
          • For example:  area = computeArea(length, width);
        • How do we turn the prompts and corresponding cin statements into a function?
          • For example:  length = promptAndGet("Please enter the length");
    • Example:  functions.cpp
• Function Rules/Restrictions
  • Functions must be declared before their first use
    • By inclusion (e.g., #include <unistd.h>)
    • By prototyping (e.g., void write(int n))
    • By actual definition (e.g., void write (int n) { cout << n; })
  • Functions are executed when called using the actual parameters (if any) to initialize the formal parameters (if any)
    • This type of parameter semantics is named:  Call-by-Value (or Copy Semantics)
    • Next week we'll learn about:  Call-by-Reference
  • Function may have a return value.
  • Formal and actual parameters need not have the same name (but they can)
    • Even if the have the same name, they are different variables
  • Control Flow
    • When a function is called, control of the program proceeds to the called function where it remains until the called function completes
      • Each called function as its own Activation Record
      • An Activation Record is (primarily) a listing of the local variables of the function
    • Example:  functions.cpp
      • Interface Specification
      • Calling a Function
      • Defining Functions
      • Visibility (or Scope)
• Preprocessor
  • Used to "include" code from other files or for conditional compilation
  • File Inclusion
    • Examples: 
      • #include <filename> - Used for system libraries
      • #include "filename" - Used for local libraries
  • Conditional Compilation
    • #define DefinedVariableName
    • Example
      • debug.cpp
        • To compile without debug code:  g++ debug.cpp -o debug
        • To compile with debug code:  g++ debug.cpp -o debug -DDEBUG
      • iostream