Mark Dixon Page 1 06 – Conditional Execution. Mark Dixon Page 2 Admin: Test (next week) In class test –teaching week 6 50 minutes short answer (5 - 6.

Mark Dixon Page 1

06 – Conditional Execution

Mark Dixon Page 2

Admin: Test (next week)• In class test

– teaching week 6

• 50 minutes

• short answer (5 - 6 words max)

• 25% of coursework mark

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Questions: Data Typesa) What is the result of:

String("George Boole").subStr(4, 4)

b) What is put in lblRes?txtPetName.value = "George"lblRes.innerText = String(txtPetName.value).slice(3, 6)

c) What is put in lblRes?txtPetName.value = "George"lblRes.innerText = String("txtPetName").subStr(0, 3)

ge B

rge

txt

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Session Aims & Objectives• Aims

– to introduce the main concepts involved in getting the computer to act differently under different circumstances

• Objectives,by end of this week’s sessions, you should be able to:

– evaluate and generate conditional expressions– use conditional statements to make your code

more adaptable

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Example: DrinksSPECIFICATION

• User Requirements – Students wish to decide which supermarket sells

drinks at the best price

• Software Requirements– Functional:

–user enters offer details (bottle size, number of bottles, and price)

–computer calculates bottle price and price per pint

– Non-functionalshould be easy to use

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Debugging• key skill:

– locate the cause of a bug• using testing methods

• first step– narrow it down as much as possible

• typical pattern in early tutorials:– student: it doesn't work– lecturer: what doesn't work– student: my code– lecturer: yes, but which bit exactly– student: ????– lecturer: run your program, take me through it, which bits work, and

where exactly does it go wrong– student: when I click this, nothing happens– lecturer: which bit of code is responsible for doing that?– student: this bit

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Example: Drinks• What happens when run?

– Nothing?

– think of murder investigationwho-done-it?

– input boxes, button, and text displaystherefore: html works!

– button click causes errortherefore: prime suspect is button code

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Example: Drinks (with ERRORS)<html> <head><title></title></head> <body> Bottle Size: <input id="txtBottleSize" type="text" />ml<br /> Quantity: <input id="txtQty" type="text" /><br /> Price (£): <input id="txtPrice" type="text" /><br /> <input id="btnCalc" type="button" value="Calc" onclick="btnCalc_onClick()" /><br /> £<span id="lblBottlePrice"></span> per bottle<br /> £<span id="lblPintPrice"></span> per pint<br /> </body></html>

<script language="javascript"> function Calc_onClick(){ lblBottlePrice.innerText = txtQty.valu / txtPrice.value; lblPintPrice.innerText = lblBottlePrice.innerText * (568 / txtBottleSize.value); }</script>

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Debugging• Examine code line by line

– can help, but time consuming

• Breakpoint (press F9 on keyboard):

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Debugging• Breakpoint: like DVD pause, when line hit

• Logic:– if breakpoint hit, code will pause,

therefore event handler is OK, must be code

– if nothing happens, breakpoint not hit,therefore event handler not working (this is what happens – check name)

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Example: Drinks (with ERRORS)<html> <head><title></title></head> <body> Bottle Size: <input id="txtBottleSize" type="text" />ml<br /> Quantity: <input id="txtQty" type="text" /><br /> Price (£): <input id="txtPrice" type="text" /><br /> <input id="btnCalc" type="button" value="Calc" onclick="btnCalc_onClick()" /><br /> £<span id="lblBottlePrice"></span> per bottle<br /> £<span id="lblPintPrice"></span> per pint<br /> </body></html>

<script language="javascript"> function Calc_onClick(){ lblBottlePrice.innerText = txtQty.valu / txtPrice.value; lblPintPrice.innerText = lblBottlePrice.innerText * (568 / txtBottleSize.value); }</script>

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Debugging: Breakpoint hit• After event-handler fixed

– breakpoint hit, code paused

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Debugging• Can run 1 line – press F8 on keyboard

Always click Break(this means pause)

Always read message

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Debugging – Stop Button• Click Stop button, to edit code

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Debugging: Check output• Is this right?

– if each bottle is 0.8,then 0.8 * quantity should be same as price

– 0.8 * 4 = 3.2

– this is wrong

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Debugging: Immediate Window• Can now ask questions

– what is in txtPrice.value

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Adaptive Behaviour• So far

– every statement always executed in sequence

• Often necessary for software to– change behaviour under different circumstances

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Example: Multiplication TestSPECIFICATION

• User Requirements – A primary school teacher wants to test the

multiplication skills of her children.

• Software Requirements– Functional:

–display a multiplication question–allow the user to type a response–check the response and provide feedback

– Non-functionalshould be interesting, colourful, and easy to use

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Example: Multiplication Test v1<html> <head><title>Multiply</title></head> <body> <p>What is 5 times 3?</p> <input id="txtAns" type="text" /><br /> <input id="btnAns" type="button" value="Check" onclick="btnAns_onClick()" /> <p id="lblComment"></p> </body></html>

<script language="javascript"> function btnAns_onClick(){ if (txtAns.value == 15){ document.bgColor = "yellow"; lblComment.innerText = "Correct, well done!"; }else{ document.bgColor = "cyan"; lblComment.innerText = "Sorry, try again"; } }</script>

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Example: Multiplication Test v1

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Example: Multiplication Test v1

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if statements• Use the following syntax (pattern):

if (condition){ statementblock}

• For example:if (txtAge.value < 18){ document.bgColor = "Red";}

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if else statements• Use the following syntax (pattern):

if (condition){ statementblock-1}else{ statementblock-2}

• For example:if (txtAge.value < 18){ document.bgColor = "Red";}else{ document.bgColor = "Blue";}

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George Boole• 1815 (Lincoln, UK) – 1864

• Invented Boolean algebra– key concept in computing– boolean datatype:

• 0 false• 1 true

• Condition – expression, evaluates to:– true (stored as –1)

– false (stored as 0)

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Conditions: Relational Operators• conditions contain relational operators:

== is equal to> is greater than< is less than>= is greater than or equal to<= is less than or equal to!= is not equal to

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Conditions: Examples (literal)• Using literals:

34 == 34

34 == 12

34 > 4

18 <= 18

"hello" > "zoo"

true

false

true

true

false

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Conditions: Examples (symbolic)• Using symbols (controls' properties):

Assume that:picMain.style.posLeft is 2300

picMain.style.posLeft == 2300

picMain.style.posLeft == 2309

picMain.style.posLeft != 189

picMain.style.posLeft > 1900

true

false

true

true

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Conditions: Errors• Are the following valid:

– 23 > 30

– 66 15

– 23 <

– picBat.style.posLeft > 1000

– < picBat.style.posTop

missing (relational) operator

missing data

missing data

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Questions: Conditions• What is the result of (picMain.style.posLeft is 5589):


• What is the result (txtAge.value is 19, txtSalary.value is 10787):txtAge.value < 21 && txtSalary.value < 10787

• Write an expression to check if:the posLeft of picMain is larger than 167

• Write an expression to check if:picMain posTop is more than picBall posTop

true

false


picMain.style.posTop > picBall.style.posTop

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Example: Student Loan<html> <head><title>Student Loan Repayment Calculator</title></head> <body> <center><font size="+2"><b>Student Loan Repayment Calculator</b></font></center> <input id="txtIncome" type="text" /> <input id="btnCalc" type="button" value="Calculate" onclick="btnCalc_onClick()" /> <p id="lblPayment"></p> </body></html>

<script language="javascript"> function btnCalc_onClick(){ lblPayment.innerText = (txtIncome.value - 15000) * 0.09; }</script>

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Example: Student Loan (v2)<html> <head><title>Student Loan Repayment Calculator</title></head> <body> <center><font size="+2"><b>Student Loan Repayment Calculator</b></font></center> <input id="txtIncome" type="text" /> <input id="btnCalc" type="button" value="Calculate" onclick="btnCalc_onClick()" /> <p id="lblPayment"></p> </body></html>

<script language="javascript"> function btnCalc_onClick(){ if (txtIncome.value > 15000){ lblPayment.innerText = "£" + ((txtIncome.value - 15000) * 0.09); }else{ lblPayment.innerText = "You pay nothing (£0.00)!"; } }</script>

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Example: Ball Char• Functional Decomposition

• Incremental Development

• Get ball char to bounce horizontally:– get ball char to appear on left of page– get ball char to move right on page (user click)– get ball char to move right on page automatically– get ball char to stop at end– get ball char to change direction

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Example: Ball Char (v2)<html> <head><title>Ball Char</title></head> <body style="background-color: Lime;" onload="window_onLoad()"> <img id="picBall" src="BallChar.gif" style="position: absolute;" /> </body></html>

<script language="javascript"> function window_onLoad(){ window.setInterval("MoveBallRight()", 50); } function MoveBallRight(){ picBall.style.posLeft = picBall.style.posLeft + 5; }</script>

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Example: Ball Char (v2.1)<html> <head><title>Ball Char</title></head> <body style="background-color: Lime;" onload="window_onLoad()"> <img id="picBall" src="BallChar.gif" style="position: absolute;" /> </body></html>

<script language="javascript"> function window_onLoad(){ window.setInterval("MoveBallRight()", 50); } function MoveBallRight(){ if (picBall.style.posLeft < document.body.clientWidth){ picBall.style.posLeft = picBall.style.posLeft + 5; } }</script>

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<script language="javascript"> function window_onLoad(){ window.setInterval("MoveBallRight()", 50); }

function MoveBallRight(){ If ((picBall.style.posLeft + picBall.width) < document.body.clientWidth){ picBall.style.posLeft = picBall.style.posLeft + 5; } }</script>

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function MoveBallRight(){ If ((picBall.style.posLeft + picBall.width + 5) < document.body.clientWidth){ picBall.style.posLeft = picBall.style.posLeft + 5; } }</script>

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function MoveBallRight(){ if ((picBall.style.posLeft + picBall.width + 5) < document.body.clientWidth){ picBall.style.posLeft = picBall.style.posLeft + 5; }else{ window.setInterval("MoveBallLeft()", 50); } }

function MoveBallLeft(){ picBall.style.posLeft = picBall.style.posLeft – 5; }</script>

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Example: Ball Char (v2.5)• Bounce from side to side, with sound:

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Example: Pizza Delivery

A Pizza shop provides a delivery service. If the delivery is within five miles of the shop, then no delivery fee is charged. If the cost of the goods is less than £10 then a £3 delivery fee is charged, otherwise a £1.50 delivery fee is charged.

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Decision Trees• Natural language

– ambiguous & difficult to follow

• Decision trees– express same information clearly

distance <= 5 miles

value >= £10

Free

£1.50

£3.00

Y

N Y

N

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Example: Pizza Delivery<html> <head><title>Delivery</title></head> <body> <p>Distance: <input type="text" id="txtDist" /><br /> Cost: <input type="text" id="txtCost" /><br /> <input type="button" id="btnCalc" value="Calc" onclick="btnCalc_onClick()" /> </p> <p id="lblCharge"></p> </body></html>

<script language="javascript"> function btnCalc_onClick(){ if (txtDist.value <= 5){ lblCharge.innerText = "Delivery Charge: £0.00"; }else{ if (txtCost.value >= 10){ lblCharge.innerText = "Delivery Charge: £1.50"; }else{ lblCharge.innerText = "Delivery Charge: £3.00"; } } }</script>

• Nested If statements– one if

inside another if

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If statements: Errors

if (txtNum.value > 5){ if (txtNum.value == 4){ document.bgColor = "green";

}

if (picMan.width > 5) document.bgColor = "red";}

missing }

missing }

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Logical Operators

• And True when both items are TruepicMain.vSpace > 5 && picMain.vSpace < 35 truepicMain.vSpace < 10 && picMain.vSpace > 55 falsepicMain.vSpace > 6 && picMain.vSpace < 23 falsepicMain.vSpace >= 6 && picMain.vSpace <= 23 true

• Or True when either item is TruepicMain.vSpace == 23 || picMain.vSpace == 11 truepicMain.vSpace < 10 || picMain.vSpace > 55 false

• Not True when item is False! (picMain.vSpace == 23) false

Use to join conditions (picMain.vSpace is 23):

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Logical Operators: Errors

if (picMan.width > 5 && < 10){ document.bgColor = "red";} missing

data

if (picMan.width > 5 && picMan.width < 10){ document.bgColor = "red";}

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Tutorial Exercises: Drinks• LEARNING OBJECTIVE:

use interactive debugger to identify and correct errors

• Task 1: Create a new project, and type in the code for the drinks example. Running it should display the html, but the calc button does nothing.

• Task 2: Use the interactive debugger to identify and correct the errors in the code.

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Tutorial Exercises: Multiplication• LEARNING OBJECTIVE:

use if statement to perform conditional execution

• Task 1: Get the Multiplication v1 examples (from the lecture) working.

• Task 2: Modify your program so that the text box is disabled after the answer is checked

• Task 3: Modify your program so that it makes a suitable sound when the user gets the answer right/wrong. Sound files are in the resources section of the web-site

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Tutorial Exercises: Student Loan• LEARNING OBJECTIVE:


• Task 1: Get the Student Loan v1 and v2 examples (from the lecture) working.

• Task 2: Modify your program so that it calculates and displays monthly income and repayment amounts (as well an annual).

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Tutorial Exercises: BallChar• LEARNING OBJECTIVE:


• Task 1: Get the BallChar example (from the lecture) working.You will need to work out the code for v2.5 – use the previous code for inspiration.

• Task 2: Modify your program so that the Ball Character blinks when the mouse moves over it

• Task 3: Modify your program to play a sound when the ball character is clicked

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Tutorial Exercises: Pizza Delivery• LEARNING OBJECTIVE:

use nested if statements to perform conditional execution

• Task 1: Get the Pizza Delivery example (from the lecture) working.

Mark Dixon Page 1 06 – Conditional Execution. Mark Dixon Page 2 Admin: Test (next week) In class test –teaching week 6 50 minutes short answer (5 - 6.

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