SUNY Geneseo Department of Mathematics

If Statements

Wednesday, March 1

Math 230 02
Spring 2017
Prof. Doug Baldwin

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Misc

Colloquium

Eleni Panagiotou, faculty candidate

“Quantifying Entanglement in Physical Systems”

Thursday, March 2, 2:30 PM, Newton 203

Extra credit for writing a paragraph or so summarizing connections you make between the talk and your own interests.

My Hectic Schedule

Starting with homework 1 (but not lab 4), if you can demonstrate by the “complete by” date that there are no appointments left in the grading window, I’ll extend the deadline for you to the earliest date on which you can make an appointment.

Homework 1 deadline is still Monday for grading.

Next Week

I’m out of town from Wednesday afternoon through the end of the week.

Friday class will (probably) be something with Nicole, but the details are still being worked out.

Questions?

If Statements

Section 11.1

If and Its Variants

Write a function of one argument that prints “this number is negative” if its argument is less than 0.

A useful new Matlab function: fprintf( message ) will print the string message to the command window.

For example, fprintf( 'Hello World\n' )
The \n pattern indicates that a new line of output starts

>> fprintf( 'Hello World\n' )
Hello World
>> fprintf( 'Hello World' )
Hello World>> fprintf( 'Hello\nWorld\n' )
Hello
World

Reading ideas:

if statements look like

if expression
...
end

This executes the statements between the expression and end if the expression is true
It ignores those statements otherwise
There are also if-else statements, which look like

if expression
...
else
...
end

This allows two options: either execute the statements between if and else if the expression is true, or execute the statements between else and end if the expression is false
There are also if - elseif - else chains of tests, that can make multiway choices:

if expression1
...
elseif expression2
...
elseif ...
...
else
...
end

Using these ideas, we can write a function that does more than asked in the original problem. This function classifies its argument as negative, zero, or positive:

function [] = negative( x )
    %NEGATIVE Identify whether x is negative, zero, or positive
    % via a printed message
    if ( x < 0 )
        fprintf( 'This number is negative\n' )
    elseif ( x == 0 )
        fprintf( 'This number is 0\n' )
    else
        fprintf( 'This number is positive\n' )
    end
end

Input

Some of you discovered Matlab’s input function, which is complementary to fprintf in that it allows a Matlab program to read something from the user.

You can use input to write a script equivalent to the negative function above (typically you don’t need input in functions, since they can and should receive their inputs via their arguments).

%% Ask user for a number and decide whether it’s positive, zero, or
% negative.

x = input( 'What is your favorite number? ' );

if ( x < 0 )
    fprintf( 'This number is negative\n' )
elseif ( x == 0 )
    fprintf( 'This number is 0\n' )
else
    fprintf( 'This number is positive\n' )
end