Notes

Outline

Announcements Project 2a due Monday Kasparov and Deep Jr. are tied

Functions & Abstraction  A function is a package for an algorithm; once written, it can be use over and over.

The Package Functions have a specific syntax  function <name> ( <parameter list> ) {           <function definition> } <name> names are identifiers; start w/letter <parameter list> is the input variables, a list separated by commas <function definition> is just the program to do the work

A Sample Function Compute the Body Mass Index when the inputs are in metric function <name> ( <parameter list> ) {           <function definition> }

Writing Functions Most programming is done by writing functions, so learning the form is key

Declarations A function is declared by writing down the “package” … the function is used when it is called

Summarizing Declaration: the function “package,” says what happens when the function runs Call: the function use, asks for the computation to be run There is only one function declaration There can be many calls … functions are reusable In JS, functions tend to be grouped together but the calls go where they are needed

Gold Function Suppose we compute “weight in Au” Worth = (Weight*12)*368.4

Gold Function Suppose we compute “weight in Au” Worth = (Weight*12)*368.4

Gold Function Suppose we compute “weight in Au” Worth = (Weight*12)*368.4

Gold Function Suppose we compute “weight in Au” Worth = (Weight*12)*368.4

Recall Testing Template No one writes perfect programs the first time … smart programmers check To test, have a standard page handy

Declare the Function Put a function declaration in <script>

Try The Function

Function Features Reviewing properties of functions Selecting names … don’t use alert() Parameter variables … don’t need to be declared, but work like local variables

Function Features (cont.) Scope of Reference … refers to where in the program a variable is “known,” i.e. where its value can be referenced and/or assigned

Function Features (cont.) Global … declared outside of functions

Function Features (cont.) Parameters vs Arguments … parameters are the “formal” variables in the function declaration; arguments are the same thing in the call

Summary Functions are packages for algorithms They follow a series of rules, that quickly become intuitive Functions have both a declaration and a call Functions have both parameters (in the declaration) and arguments (in the call) Scope refers to the region of a program where a variable is “known”