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