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College of EngineeringEngineering Education Innovation Center

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More Script Files in MATLAB

Script File I/O : Chapter 4

1. Global Variables

2. The Input Command

3. The Disp Command

4. The fprintf Command

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Global Variables Command window and script file variables are

Global Variables

Global variables are variables that, once created in

one part of MATLAB (e.g. command window), are

recognized and valid in other parts of MATLAB (e.g.

script file).

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INPUT TO A SCRIPT FILE

3 ways to input data to a script file:

1. Define variable in script file (hardwired or hardcoded)

To change variable:

Edit script file, and change the value of the variable

Save script file

Execute script file

2. Define variable in command window (global variable)

To change variable:

Type new value for variable in command window

Execute script file

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INPUT TO A SCRIPT FILE

3. Interactively with userTo change variable:

Execute script file

Enter new value when prompted

x = input(‘text’)

string

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This third option is done by using the input() function:

The input function will: display the string ‘text’ in the command window and wait. assign what is entered in the command window to the variable x.

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Interactive Example

For example:

(script file)x = input(‘Please enter a value for x: ’)

Please enter a value for x: 5x = 5

User Input

(command window)

Note the space: it makes the command window more readable

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Input Statement Examples

Given the MATLAB command,

what is typed in the command window can be any valid MATLAB statement.

x = input('Please enter a value for x: ')

Please enter a value for x: 'String'Please enter a value for x: [1 2 3]B=5;Please enter a value for x: BA=3;Please enter a value for x: A*B

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The 's' optionAs you have seen, text typed into the

command window in response to an input command without single quotes to indicate a string will be interpreted as a variable name. The 's' option, tells the input function to interpret whatever is typed as a string, i.e.

Thus the user does not need to even know what a string is. Adding modifiers as a single character is common in MATLAB.

x = input('Please enter a value for x: ', 's')

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OUTPUT FROM A SCRIPT FILE

When a script file runs, output that is generated is

displayed in the Command Window

Output is displayed automatically if a statement does

not end with a semicolon. Many times you don’t want all

outputs to be displayed in the command window.

Output can also be displayed intentionally by using the

disp() command

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THE disp() COMMAND

disp(A)

disp(‘text’)

string

disp() adds a ‘line feed’ to the end of it’s input. So, any following output appears on a new line.

Displays the value of the variable A.

Displays the text (string) that is

enclosed within the single quotes.

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SCRIPT FILE INPUT/OUPUTChapter4Example5 Script file

%This scipt file calculates the average points scored

%in three games. The points from each game are assigned

%to the variable by using the input() command.

%The disp() command is used to display the output

game1 = input(‘Enter the points scored in the first game ‘);

game2 = input(‘Enter the points scored in the second game ‘);

game3 = input(‘Enter the points scored in the third game ‘);

ave_points = (game1 + game2 + game3) / 3;

disp(‘ ‘)

disp(‘The average points scored in a game is:’)

disp(‘ ‘)

disp(ave_points)

Display empty line

Display Text

Display the value of the variable ave_points

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Note ;

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EXAMPLE OF RUNNING A SCRIPT FILE WITH INPUT/OUPUT

Command Window:>> Chapter4Example5Enter the points scored in the first game 89Enter the points scored in the second game 60Enter the points scored in the third game 82

The average points scored in a game is:

77

>>

The scores are enteredfollowing the prompt

Display empty line

Display text

Display the values of variable ave_points

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CREATE AND DISPLAY A TABLE

YEAR POPULATION

(MILLIONS)

1984 127

1986 130

1988 136

1990 145

1992 158

1994 178

1996 211

How would you create the table format of data as shown in this slide?

Heading (first line)

Heading (second line)

Empty Line

The array tableYP

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CREATE AND DISPLAY A TABLE

yr = [1984: 2: 1996];

pop = [127 130 136 145 158 178 211];

tableYP(:, 1) = yr’;

tableYP(:, 2) = pop’;

disp(‘ Year Population’)

disp(‘ (millions)’)

disp(‘ ‘)

disp(tableYP)

The year and population data is entered in two row vectors

yr is entered as the first column in array tableYP

pop is entered as the second column

Display heading (first line)

Display heading (second line)

Display an empty line.

Display the array tableYP

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In it’s simplest form, fprintf looks a lot like disp, with control characters

Control Characters:\n starts a new line\b backspace\t horizontal tab

fprintf does not automatically add a ‘line feed’ you must include a \n

fprintf ('text typed as a string \n')

The fprintf command

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fprintf ('text %-5.2f more text', variable_name)

The fprintf command

% marks where to insert a number- is a flag to left justify

(other choices + to add a sign, 0 pads with 0’s)

5 is the number of spaces on the page to reserve for the number

2 is the number of digits after the decimal point

f is the number format(e,E,g,G,i)

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fprintf ('text … %f more text … %geven more text … %e last text‘,

var_1,var_2,var_3)

The fprintf command

More than one variable can be printed

Control characters can be used to help arrange appearance

Without a \n, subsequent fprintf commands will not start on a new line!

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Tables can be printed with more control over spacing and how numbers appear

If there are more numbers to be printed than described in the 'text' portion of an fprintf statement, then the statement will be used over and over until all numbers are displayed.

fprintf ('header line 1 \n header line 2 \n')fprintf (' %5i %5.2f \n', tableYP')

The fprintf command

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The 'text' portion of the data fprintf should describe the data line layout

Arrays are displayed column by column. If an array is arranged the way you want a table to appear, as with tableYP in the previous disp example, then you need to transpose it for fprintf!

fprintf ('header line 1 \n header line 2 \n')fprintf (' %5i %5.2f \n', tableYP')

The fprintf command