Modular Programming Functions ICS 3 U Theory Purpose

Modular Programming Functions ICS 3 U

Theory • Purpose: To break a large problem into manageable pieces • Advantages – Easier to Understand – Easier to Modify and Debug – Reduces Repetitive Code – Build modules to be reused by other programs – Divide project among team members

Functions • Functions are the programming constructs that allow us to create modularity • You have been using functions since day 1 in this course: – pow – built-in function – calculates a power when given a base and an exponent value (Math class functions) – parse. Int – built in function – converts text to integer – The standard library is filled with built-in functions – written functions to be executed upon the click of the mouse, or entry from the keyboard

Using a Function • In order to create and use a function – they need to be defined and called. • A function definition is the actual code of the function. • It specifies: – The inputs to the function – The logic of the function – The output of the function (in some languages)

Function Definition in Action. Script Keyword function Identifier – programmer makes this in order to refer to the function nameoffunction(parameters) { Parameters – input into the function code statements; Only thing new in this is }; the parameters. . . !!!! Body of the function Declare variables and write the logic for the function

Example: Function Definition function bigger(firstnum, secondnum) { var largest: int; if (firstnum > secondnum) { largest = firstnum; } else { largest = secondnum; } return largest; } function name = bigger Parameters = firstnum, secondnum Values are passed into this function Largest – local variable Declared in this function. . . Can only be used in this function Return largest – output of the function Value is passed back to where the function was called from. Functions can only return one value.

Function Calls • Functions are called by using it name and giving the proper inputs. • Examples: go_mc. add. Event. Listener(Mouse. Event. CLICK, go. Clicked); answer = Math. pow(3, 0. 5); trace(bigger(num 1, num 2)); • A function needs to be passed the correct information or an error will occur!

Example: Calling the Function Bigger go_mc. add. Event. Listener(Mouse. Event. CLICK, go. Clicked); function go. Clicked(e: Mouse. Event) { Note: num 1 and num 2 are local variables. They are passed into bigger where their values are transferred to var num 1: int; the variables firstnum and secondnum var num 2: int; num 1 = parse. Int(txtnum 1_text); num 2 = parse. Int(txtnum 2_text); } trace("The larger number is. . . " + bigger(num 1, num 2)); Because return is used in the function this function call will output the larger number.

Other Important Points • Global Variables – Variables declared at the start of the program. Exit throughout the program • Local variables – Variables declared inside a function. They do not exist outside of the function. • Considered good style to minimize global variables. Making modules more self-contained. • Data shared between functions should be “passed” using parameters.

Exercises Draw Triangle Fraction Math Add Times Descriptions on the Website!!