General Computer General Computer Science Science

for Engineersfor EngineersCISC 106CISC 106

Lecture 04Lecture 04

Roger CraigComputer and Information Sciences

9/11/2009

Lecture ObjectivesLecture ObjectivesIf statements (nested)Logical OperatorsMatlab Output

IF StatementsNested if statements can be used

when two things have to be true for a command to execute

IF StatementsUsing nested if

statements

if (x < 5)

if ( x > 2)

y = 500

else

y = 300

end

else

y= 200

end

IF StatementsUsing nested if

statements

if (x < 5)

if ( x > 2)

y = 500

else

y = 300

end

else

y= 200

end

Using multiple conditions in one if statement

if ( x < 5 & x > 2)

y = 500

else

y = 200

end

Logical Operators - AND

&

&&

A & BA

T F

BT T F

F F F

Logical Operators - OR

|

||

A | BA

T F

BT T T

F T F

Logical Operators - NOT~

~A

T F

F T

Numbers as True/FalseWhat do you think would happen

here:

if (5)

disp(‘5 is a true value’);

else

disp(‘5 is a false value’);

end

Numbers as True/False Group activity: evaluate the

following as true or false for x=5:

1. x < 7 & 3 < x2. ˜(x / 2 > 1 & x < 0)3. x ˜= 5 & x + 2 > 6 | x > 54. x + x == 2 * x && ˜x

Matlab Output◦ How do we see information about what is going on

in our program?

Matlab Output◦ How do we see information about what is going on

in our program?

◦ disp()

Matlab OutputFormatted OutputExample:

◦ “There are 5 widgets in inventory”◦ fprintf(‘There are %d widgets in inventory’,

widgets);

Matlab OutputFormatted OutputExample:

◦ “There are 5 widgets in inventory”◦ fprintf(‘There are %d widgets in inventory’,

widgets);%d acts as a place holder for widget variable at end

of command and is known as a conversion character.

Conversion characters specify the notation of the output.

Note the variable widgets as the second argument.

Matlab Output

Lets look at the syntax◦count = fprintf(fid, format, A, ...)◦count – the number of bytes written◦fid – refers to opened file◦format – is a format string in between

single quotesIf fid is set to one or omitted the output goes

to the screen.

Arrays

ArraysArrays

ArraysArraysFundamental unit of data in MATLABCollection of data into rows and

columns(MATrix LABoratory)1 dimensional, vector2 dimensional, matrix0 dimensional, scalar (a 1x1 array)

Row vector, column vector , transpose

ArraysArrays

Array commandsArray commandsa = [1 2 3 4]b = [1; 2; 3; 4]c = [1 2; 3] (error)d = [1 2; 3 4]f = d(1,2)g(4,5) = 7

Arrays continuedArrays continuedzeros(), ones(), eye()scalar vs. array arithmetic

+, - , * (.*) , / (./) ^ etc.