General Computer Science General Computer Science for Engineersfor Engineers

CISC 106CISC 106Lecture 02Lecture 02

James AtlasComputer and Information Sciences

6/10/2009

Lecture OverviewLecture OverviewHow does our program work?

More on VariablesMore on ExpressionsMore on FunctionsM-files

-    Scripts versus functions

How does our program work?CPU

Disk

Memory

Putting it together

VariablesVariablesvar = expression

x = 2 * 2comment = ‘This is a string’area = circleArea(5)

VariablesVariablesvar = expression

x = 2 * 2comment = ‘This is a string’area = circleArea(5)

What type of data is stored in each variable?

ExpressionsData + Operator

◦2 + 2◦circleArea(5)

Our ringArea(rad1, rad2)

function out=ringArea(radius1, radius2)area1 = circleArea(radius1);area2 = circleArea(radius2);out = area1 - area2;

Can you think of a simpler way to write this?

ExpressionsData + Operator

◦2 + 2◦circleArea(5)

Nested Expressions◦circleArea(5) + circleArea(3)

FunctionsFunctionsAnalogous to mathematical

functions◦f(x) = x + 1

Each function is like a mini-program within the larger program itself

Key to breaking problems down

FunctionsFunctionsIn MATLAB, the first line of a function

takes the following form:function <return value> =

<name>(<arguments>)

Functions cont.Functions cont.The first line of a function:function <return value> =

<name>(<arguments>)

The return value can be a number, a string, a matrix, etc.

Arguments ◦Can be a list of zero or more variables ◦ Can also be numbers, strings, matrices

FunctionsFunctionsFunctions can call other functions

Like in class on Monday:

function outputValue = ringArea(rad_1, rad_2)

outputValue = circleArea(rad_1) - circleArea(rad_2);

FunctionsFunctionsBreak down problems into

subproblems◦Decomposition

How big/small should a function be?

Problem SolvingProblem SolvingMP3 player

◦Store song lists, store playlists, import/export songs, shuffle play, repeat play, etc.

Bank ATM SoftwareBank ATM SoftwareWhat are inputs and outputs?Inputs:Output:

Bank ATM SoftwareBank ATM SoftwareWhat functions might we need?

Bank ATM SoftwareBank ATM SoftwareWhat functions might we need?

Break it down even more?

M-filesM-filesA script file

◦Store commands in◦Running a script file (m-file)

A function file◦Special type of m-file◦Contains a function name,

arguments, etc., and implementation

Scripts vs. functionsScripts vs. functionsFunctions have input and output

parametersScripts are a sequence of commands

Functions are more flexibleFunction files have one function per

file