Mark Dixon 1 06 – Conditional Execution

Mark Dixon 2 Admin: Test (next week) In class test –teaching week 7 50 minutes short answer (5 - 6 words max) 25% of overall mark

Mark Dixon 3 Questions: Data Types a)What is the result of: Mid("George Boole", 5, 4) b)What is put in lblRes? txtPetName.value = "George" lblRes.innerText = Right(txtPetName.value, 3) c)What is put in lblRes? txtPetName.value = "George" lblRes.innerText = Right("txtPetName", 3) ge B rge ame

Mark Dixon 4 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 (If) to make your code more adaptable

Mark Dixon 5 Example: Drinks SPECIFICATION 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-functional should be easy to use

Mark Dixon 6 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

Mark Dixon 7 Example: Drinks What happens when run? –Nothing? –think of murder investigation who-done-it? –input boxes, button, and text displays therefore: html works! –button does not respond therefore: prime suspect is button code

Mark Dixon 8 Example: Drinks (with ERRORS) Bottle Size: ml Quantity: Price (£): £ per bottle £ per pint Sub Calc_onClick() lblBottlePrice.innerText = txtQty.valu / txtPrice.value lblPintPrice.innerText = lblBottlePrice.innerText * (568 / txtBottleSize.value) End Sub

Mark Dixon 9 Debugging Examine code line by line –can help, but time consuming Breakpoint (press F9 on keyboard):

Mark Dixon 10 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)

Mark Dixon 11 Example: Drinks (with ERRORS) Bottle Size: ml Quantity: Price (£): £ per bottle £ per pint Sub Calc_onClick() lblBottlePrice.innerText = txtQty.valu / txtPrice.value lblPintPrice.innerText = lblBottlePrice.innerText * (568 / txtBottleSize.value) End Sub

Mark Dixon 12 Debugging: Breakpoint hit After event-handler fixed –breakpoint hit, code paused

Mark Dixon 13 Debugging Can run 1 line – press F8 on keyboard Always click Break (this means pause) Always read message

Mark Dixon 14 Debugging – Stop Button Click Stop button, to edit code

Mark Dixon 15 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 –therefore: bottle price must be wrong

Mark Dixon 16 Debugging: Immediate Window Can now ask questions –what is in txtPrice.value

Mark Dixon 17 Adaptive Behaviour So far –every statement always executed in sequence Often necessary for software to –change behaviour under different circumstances

Mark Dixon 18 Example: Multiplication Test SPECIFICATION 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-functional should be interesting, colourful, and easy to use

Mark Dixon 19 Example: Multiplication Test v1 Multiply What is 5 times 3? Sub btnAns_OnClick() If txtAns.value = 15 Then document.bgColor = "yellow" lblComment.innerText = "Correct, well done!" Else document.bgColor = "cyan" lblComment.innerText = "Sorry, try again" End If End Sub

Mark Dixon 20 Example: Multiplication Test v1

Mark Dixon 21 Example: Multiplication Test v1

Mark Dixon 22 If Then statements Use the following syntax (pattern): If condition Then statementblock End If For example: If txtAge.value < 18 Then document.bgColor = "Red" End If

Mark Dixon 23 If Then Else statements Use the following syntax (pattern): If condition Then statementblock-1 Else statementblock-2 End If For example: If txtAge.value < 18 Then document.bgColor = "Red" Else document.bgColor = "Blue" End If

Mark Dixon 24 George Boole 1815 (Lincoln, UK) – 1864 Invented Boolean algebra –key concept in computing –boolean datatype: false(stored as 0) true(stored as 1 or -1) Condition – Boolean expression, evaluates to true or false

Mark Dixon 25 Conditions: Relational Operators conditions contain relational operators: =is equal to >is greater than =is greater than or equal to is not equal to

Mark Dixon 26 Conditions: Examples (literal) Using literals: 34 = = > 4 18 "zoo" true false true false

Mark Dixon 27 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

Mark Dixon 28 Conditions: Errors Are the following valid: – 23 > 30 – – 23 < – picBat.style.posLeft > 1000 – < picBat.style.posTop   missing (relational) operator missing data  missing data

Mark Dixon 29 Questions: Conditions What is the result of (picMain.style.posLeft is 5589): picMain.style.posLeft > 4400 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 picMain.style.posLeft > 167 picMain.style.posTop > picBall.style.posTop

Mark Dixon 30 Example: Student Loan Student Loan Repayment Calculator Student Loan Repayment Calculator Sub btnCalc_onClick() lblPayment.innerText = (txtIncome.value ) * 0.09 End Sub

Mark Dixon 31 Example: Student Loan (v2) Student Loan Repayment Calculator Student Loan Repayment Calculator Sub btnCalc_onClick() If txtIncome.value > Then lblPayment.innerText = "£" & ((txtIncome.value ) * 0.09) Else lblPayment.innerText = "You pay nothing (£0.00)!" End If End Sub

Mark Dixon 32 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

Mark Dixon 33 Example: Ball Char (v2) Ball Char Sub window_onLoad () window.setInterval "MoveBallRight()", 50 End Sub Sub MoveBallRight () picBall.style.posLeft = picBall.style.posLeft + 5 End Sub

Mark Dixon 34 Example: Ball Char (v2.1) Ball Char Sub window_onLoad() window.setInterval "MoveBallRight()", 50 End Sub Sub MoveBallRight() If picBall.style.posLeft < document.body.clientWidth Then picBall.style.posLeft = picBall.style.posLeft + 5 End If End Sub

Mark Dixon 35 Example: Ball Char (v2.2) Ball Char Sub window_onLoad() window.setInterval "MoveBallRight()", 50 End Sub Sub MoveBallRight() If (picBall.style.posLeft + picBall.width ) < document.body.clientWidth Then picBall.style.posLeft = picBall.style.posLeft + 5 End If End Sub

Mark Dixon 36 Example: Ball Char (v2.3) Ball Char Sub window_onLoad() window.setInterval "MoveBallRight()", 50 End Sub Sub MoveBallRight() If ( picBall.style.posLeft + picBall.width + 5) < document.body.clientWidth Then picBall.style.posLeft = picBall.style.posLeft + 5 End If End Sub

Mark Dixon 37 Example: Ball Char (v2.4) Ball Char Sub window_onLoad() window.setInterval "MoveBallRight()", 50 End Sub Sub MoveBallRight() If (picBall.style.posLeft + picBall.width + 5) < document.body.clientWidth Then picBall.style.posLeft = picBall.style.posLeft + 5 Else window.setInterval "MoveBallLeft()", 50 End If End Sub Sub MoveBallLeft () picBall.style.posLeft = picBall.style.posLeft - 5 End Sub

Mark Dixon 38 Example: Ball Char (v2.5) Bounce from side to side, with sound:

Mark Dixon 39 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.

Mark Dixon 40 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

Mark Dixon 41 Example: Pizza Delivery Delivery Distance: Cost: Sub btnCalc_onClick() If txtDist.value <= 5 Then lblCharge.innerText = "Delivery Charge: £0.00" Else If txtCost.value >= 10 Then lblCharge.innerText = "Delivery Charge: £1.50" Else lblCharge.innerText = "Delivery Charge: £3.00" End If End Sub Nested If statements –one if inside another if

Mark Dixon 42 If statements: Errors If txtNum.value > 5 Then If txtNum.value = 4 Then document.bgColor = "green" End If If picMan.width > 5 document.bgColor = "red" End If missing Then keyword missing End If

Mark Dixon 43 Logical Operators AndTrue when both items are True picMain.vSpace > 5 AND picMain.vSpace 55 false picMain.vSpace > 6 AND picMain.vSpace = 6 AND picMain.vSpace <= 23 true OrTrue when either item is True picMain.vSpace = 23 OR picMain.vSpace = 11 true picMain.vSpace 55 false NotTrue when item is False Not (picMain.vSpace = 23) false Use to join conditions (picMain.vSpace is 23):

Mark Dixon 44 Logical Operators: Errors If picMan.width > 5 And < 10 Then document.bgColor = "red" End If missing data If picMan.width > 5 And picMan.width < 10 Then document.bgColor = "red" End If

Mark Dixon 45 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.

Mark Dixon 46 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

Mark Dixon 47 Tutorial Exercises: Student Loan LEARNING OBJECTIVE: use if statement to perform conditional execution 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).

Mark Dixon 48 Tutorial Exercises: BallChar LEARNING OBJECTIVE: use if statement to perform conditional execution 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

Mark Dixon 49 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.