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Mark Dixon Page 1
04 – Information Processing:Expressions, Operators & Functions
Mark Dixon Page 2
Questions: Events
• Consider the following code:
a) How many unique events does it contain?
b) Name the event(s).
function btnAns_OnClick(){ document.bgColor = "yellow"; lblComment.innerText = "Correct, well done!"; document.bgColor = "cyan"; lblComment.innerText = "Sorry, try again";}
1
ClickOnClick
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function btnAns_OnClick(){ document.bgColor = "yellow"; lblComment.innerText = "Correct, well done!"; document.bgColor = "cyan"; lblComment.innerText = "Sorry, try again";}
Questions: Properties
• Consider the following code:
a) How many unique properties does it contain?
b) Name the properties.
2
bgColor, innerText
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function btnAns_OnClick(){ document.bgColor = "yellow"; lblComment.innerText = "Correct, well done!"; document.bgColor = "cyan"; lblComment.innerText = "Sorry, try again";}
Questions: Keywords
• Consider the following code:
a) How many unique keywords does it contain?
b) Name the keywords.
1
function
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Session Aims & Objectives• Aims
– Introduce you to main processing concepts, i.e. errors, expressions, operators and functions
• Objectives,by end of this week’s sessions, you should be able to:
– identify and correct common errors– identify inputs, outputs, and processes of simple
problems– evaluate expressions– assign a value to a object's property,
• using combination of literal values, operators, functions, and identifiers
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Testing & Debugging: Errors
– syntax: computer unable to understand your instructions (program does not execute), e.g.
– run-time: program can't execute instruction and exits (future lecture)
– logical: program executes but does not match specification (do what was intended), e.g.
• 3 error types :
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• Code cannot be understood
Errors: Syntax
missing ( syntax error
• Click Yes
• keyboard cursor moves to error
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• Code cannot be executed (ignored)
Errors: Run time
• Computer – just symbol
matching– No intelligence
missing e run time error
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Errors: Logical• Code does not do what you wanted
blue insteadof red
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Questions: Errors• Spot the errors (you
should find 6), and
• decide whether they are syntax or logical
<html> <head><title>Hello</title></head> <body onclick="window_onClick()"> <input type="button" id="btnRed" Value="Red" onclick="btnRed_onClick()" /> <input type="button" id="btnBlue" Value="Blue" onclick="btnBlue_onClick()" /> <p id="lblHello"></p> </body></html>
<script language="JavaScript"> function btnBlue_onCluck(){ document.bgColor = "Red"; }
function btnRed_onlick(){ document.bgColor "Red"; }
function Window_onClick(){ document.bgColour = "White"; }</script>
JavaScriptis case sensitive
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Meet George
• Common Boa Constrictor– boa constrictor imperator
• Native toCentral & SouthAmerica
• No venom(no poison)
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Looking after George
• Problem:– Difficult to keep– Require temperature and humidity controlled
environment– Much of the literature is from the US
• Temperature in Fahrenheit: 80-85F day, 78F minimum at night (P Vosjoli 1998)
• Solution– Need a program to convert from Celsius to
Fahrenheit
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Example: Temp•User Requirements
– describe user's objectivesno mention of technology
•Software Requirements– Functional
• list facilities to be provided (often numbered)
– Non-functional• list desired characteristics
(often more subjective)
SPECIFICATION• User Requirements
– help snake keeper convert from Fahrenheit to Celsius
• Software Requirements– Functional:
–enter Fahrenheit value
–display Celsius value– Non-functional
should be quick and easy to use
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Information Processing• All computing problems:
Input Data Process Output Data
9
716+
following this pattern:
for example: to add two numbers: 7 + 9 = 16
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Information Processing (cont.)• Hence, to solve any computing problem ask:
– Input: what information goes in?
– Process: what is done to it
– Output: what information comes out
Temperature in Fahrenheit
Temperature in Celsius
9
5)32( f
c
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• To convert from Fahrenheit to Celsius:
e.g. Fahrenheit is:
Example: Temp (processing)
9
5)32( f
c
9
5)3250( c
c = 10
50
9
518
9
90
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Operators
• Operators sit between the data = assignment operator
5 + 2 addition operator result is 7 5 - 2 subtraction operator result is 3 5 * 2 multiplication operator result is 10 5 / 2 division operator result is 2.5
9
5)32( f
c
c = ((f – 32) * 5) / 9convert mathematical symbols into operators
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Example: Temp (User Interface)
<html> <head><title>Temperature</title></head> <body> <p>Fahrenheit: <input id="txtFah" type="text" style="background-color: lime" /> <input id="btnCalc" type="button" value="Calculate" /></p> <p id="parCel" style="background-color: Yellow; width: 100px;">0</p> </body></html>
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Maths with Objects
c = ((f – 32) * 5) / 9
parCel.innerText = ((txtFah.value - 32) * 5) / 9
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Example: Temp (code)<html> <head><title>Temperature</title></head> <body> <p>Fahrenheit: <input id="txtFah" style="background-color: lime" type="text" /> <input id="btnCalc" type="button" value="Calculate" onclick="btnCalc_onClick()" /></p> <p id="parCel" style="background-color: Yellow; width: 100px;">0</p> </body></html>
<script language="JavaScript"> function btnCalc_onClick(){ parCel.innerText = ((txtFah.value - 32) * 5) / 9; }</script>
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Expression Evaluation
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• The following assignment statement: parCel.innerText = ((txtFah.value - 32) * 5) / 9
contains an expression
Expressions
• Given: txtFah.Value = 68can evaluate expression:parCel.innerText = ((txtFah.value - 32) * 5) / 9 = ((68 - 32) * 5) / 9 = (36 * 5) / 9 = (180 / 9 = 20
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Expression Errors
many peopleinstinctively knowthese are wrong
data
operator
data data data
operator operator
23 + 11 - txtNum1.value * 2
34 + * 12 + txtNum1.value d o o d o d
txtNum1.value + 1 – 21 45 d o d o d d
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Example: Ball Char (v2)
• Functional Decomposition
• Incremental Development
• Get ball char to move automatically:– 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
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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>
Procedure name
Interval(in milliseconds: 1000 = 1s)
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Functions & Operators
• Used to:– process (manipulate) data
• Both Functions & Operators:– take input data/parameters (1 or more item)– process it– return a result
• which replaces the expression (substitution)
Parameter(s) Result
sqrt
Function
(16) 4
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Functions (cont.)• Functions: come before the data (which is
in brackets) sqrt(16) square root result is 4
abs(-23) absolute value result is 23
floor(2.543) integer result is 2
sin(3.1) sine result is 0.998
cos(0) cosine result is 1
random() random number result 0 to 0.99999...
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Questions: Expressionsa) What is the result of:
Math.floor(12.93) / 2
b) What is the result of:
1 + Math.floor(5.76786) + Math.sqrt(Math.floor(9.4523))
c) Write an expression to:
give the square root of 9
d) Write an expression to:
give the integer value of 16.7658765
6
1 + 5 + 3 = 9
Math.sqrt(9)
Math.floor(16.7658765)
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Problem solving: Pseudo-code
• To solve problem– think about how
you would solve it manually (without computer)
– think of steps you would take
When btnGo is clicked, Read txtNum Add 6 Put in parRes
function btnGo_onClick(){ parRes.innerText = txtNum.value + 6;}
• Convert to code
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Question: Pseudo-code
• Write VBScript code that does the following:
when btnAdd is clicked read txtAge add 1 put in parNewAge
function btnAdd_onClick(){ parNewAge.innerText = txtAge.value + 1;}
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Tutorial Exercises: Temperature• LEARNING OBJECTIVE:
to assign a value to a object's property,• using combination of literal values, operators, functions, and
identifiers
• Task 1: get the temperature example working• Task 2: modify the temperature example so that it has two extra buttons – a
plus and minus to increase and decrease the input temperature (Fahrenheit)
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Tutorial Exercises: Ball Char• LEARNING OBJECTIVE:
to assign a value to a object's property,• using combination of literal values, operators, functions, and
identifiers
• Task 1: get the ball char (v2) example working• Task 2: add a button that resets the ball char's horizontal position to 0• Task 3: add a text box that allows the user to control the speed of the ball
character. HINT: Currently, the ball char will always move 5 pixels at a time.
• Task 4: add a button that stops the ball char moving. HINT: button should put 0 into the text box
• Task 5: add two buttons – one for fast and one for slow• Task 6: add two more buttons – one for fast backwards and one for slow
backwards• Task 7: use the properties window to hide the speed text box.
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