CIS 101: Computer Programming
and Problem Solving
Lecture 4
Usman 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
Input data
Function File
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 memory
space accessible
by all scripts and
functions
Local space
for function A
Local space
for 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