cis 101: computer programming and problem solving lecture 4 usman roshan department of computer...

CIS 101: Computer Programming and Problem Solving

Lecture 4Usman Roshan

Department of Computer Science

NJIT

Overview

• So far we have seen how to define basic mathematical expressions and how to manipulate arrays and matrices

• Now we will look at script files and functions. They are useful for storing sets of commands and defining them apriori. Also an important step before we get into programming with control and flow operators

• Today: chapters 4 and 6

Scripts

• Used for writing programs

• Script variables are global. They can be accessed and modified from anywhere

Creating scripts

Editor for scripts

Running script

Output of script

Script for mean of three numbers

Output of mean script

fprintf command

• A powerful command

• General syntax

fprintf(‘text as string %-5.2f additional text’, variable name)

Formatting elements

Updated mean script

Output of updated mean script

Writing to a file

• fid = fopen(‘file_name’, ‘permission’)

• File permissions– r = open for reading– w = open for writing (if file exists then content

is deleted)– a = open for appending

Mean script output to file

Mean script output to file

Output file of mean script

Function files

Function FileInput data Output

Function syntax

function [output arguments] = function_name(input arguments)

Example functions:

function [A] = RectArea(x, y)

function [V, S] = SphereVolArea(r)

Local and global variables

• So far ALL variables we have worked with have been global. This means they can be accessed and modified by any part of the program

• In functions variables are local by default (and global if they are defined as such)

Memory space

Global memoryspace accessibleby all scripts andfunctions

Local spacefor function A

Local spacefor function B

Defining and calling a function

• A function file must be saved before it can be used.

• The name of the file must be the same as the function name

• Examples:– Function Filename– function [A] = RectArea(x,y) RecArea.m– function[V, S] = SphereVolArea(r) SphereVolArea.m

Function for computing area of sphere

Area of sphere

It won’t run if you click on the run button

Area of sphere

The function is called from the command line…

Area of sphere

Or the function can be called from a script.

Area of sphere

Function output from script

Comparison between functions and scripts

• Both scripts and funtion files are saved with .m extension

• The first line in a function file is the definition line• Function variables are local whereas script ones

are global• Function files can accept data through input

arguments and can return data similarly• When a function file is saved, the name of the

file should be the same as the function’s.

Inline functions

name = inline(‘math expression typed as a string’)

name = inline(‘math expression’, arg1, …, argn)

For example,

double = inline(‘2*x’)

defines a function that doubles the input. So

double(10) = 20

Using inline to define area of sphere