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02 – Information Processing
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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"; parComment.innerText = "Correct, well done!"; document.bgColor = "cyan"; parComment.innerText = "Sorry, try again"; } 1 Click OnClick
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Questions: Properties
Consider the following code: a) How many unique properties does it contain? b) Name the properties. function btnAns_OnClick(){ document.bgColor = "yellow"; parComment.innerText = "Correct, well done!"; document.bgColor = "cyan"; parComment.innerText = "Sorry, try again"; } 2 bgcolor, innertext
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Questions: Keywords Consider the following code:
a) How many unique keywords does it contain? b) Name the keywords. function btnAns_OnClick(){ document.bgColor = "yellow"; parComment.innerText = "Correct, well done!"; document.bgColor = "cyan"; parComment.innerText = "Sorry, try again"; } 1 function
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Session Aims & Objectives
Introduce you to main processing concepts, i.e. expressions, operators and functions Objectives, by end of this week’s sessions, you should be able to: 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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George the Snake Common Boa Constrictor
boa constrictor imperator Native to Central & South America No venom (no poison)
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Looking after George Problem: Solution Difficult to keep
Require temperature and humidity controlled environment Much of the literature is from the US Temperature in Fahrenheit: F day, 78F minimum at night (P Vosjoli 1998) Solution Need a program to convert from Celsius to Fahrenheit
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Example: Temp (Analysis)
User Requirements describe user's objectives no 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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Problem solving: Pseudo-code
To solve problem think about how you would solve it manually (without computer) think of steps you would take Convert to code When btnGo is clicked, Read txtNum Add 6 Put in parRes function btnGo_onClick(){ parRes.innerText = txtNum.value + 6; }
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Question: Pseudo-code
Write JavaScript code that does the following: when btnAdd is clicked read txtAge add put in parNewAge function btnAdd_onClick(){ parNewAge.innerText = txtAge.Value + 1; }
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Information Processing
All computing problems: following this pattern: Input Data Process Output Data for example: to add two numbers: = 16 9 7 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
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Example: Temp (processing)
To convert from Fahrenheit to Celsius: e.g Fahrenheit is: 50 c = 10
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Operators Operators sit between the data = assignment operator addition operator result is subtraction operator result is 3 5 * multiplication operator result is / division operator result is 2.5 convert mathematical symbols into operators c = ((f – 32) * 5) / 9
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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) function btnCalc_onClick(){
<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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Expressions The following assignment statement: parCel.innerText = ((txtFah.value - 32) * 5) / 9; contains an expression Given: txtFah.Value = 68; can evaluate expression: parCel.innerText = ((txtFah.value - 32) * 5) / 9; = (( ) * 5) / = (36 * 5) / = (180 / =
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Expression Errors 23 + 11 - txtNum1.Value * 2
data operator txtNum1.Value * 2 34 + * 12 + txtNum1.Value d o o d o d many people instinctively know these are wrong txtNum1.Value + 1 – d o d o d d
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Programming vs. Maths 2 In maths: x = y * 2 y * 2 = x Are the same
In programming: txtX.value = txtY.value * 2; txtY.value * 2 = txtX.value; left side is destination – cannot have expression
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Functions Function Used to: Functions (& Operators):
process (manipulate) data Functions (& Operators): take input data/parameters (1 or more item) process it return a result which replaces the expression (substitution) input Function output sqrt (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 cos(0) cosine result is 1 random() random number result 0 to
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Questions: Expressions
What is the result of: Math.floor(12.93) / 2 Write an expression to: give the integer value of txtNum Write a line of code to: put the square root of 9 into txtRes 6 Math.floor(txtNum.value) txtRes.value = Math.sqrt(9)
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Example: Student Loan (Analysis)
What: Calculate annual student loan repayment from salary How: Algorithm: read annual salary deduct £21000 calculate 9% display result Plan 2
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Example: Student Loan (Design)
When Calculate button is clicked: read annual salary text box deduct £21000 calculate 9% put result in paragraph Test Data: Input Process Output £21000 ( )* = £0 £22000 ( )* = £90
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Break
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Session Aims & Objectives
to introduce the idea of types of data introduce you to the interactive debugger Objectives, after this week’s sessions, you should be able to: recognise different types of data numeric string (text) correct errors relating to data types Use Debugger to locate and fix errors
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Example: AddNum v1 Doesn't work! plus not doing what we expect
<html> <head><title>Add Numbers</title></head> <body> <input id="txtNum1" type="text" /><br /> <input id="txtNum2" type="text" /><br /> <input id="btnAdd" type="button" value="Add" onclick="btnAdd_onClick()" /> <p id="parResult"></p> </body> </html> <script language="JavaScript"> function btnAdd_onClick(){ parResult.innerText = txtNum1.value + txtNum2.value; } </script> Doesn't work! plus not doing what we expect
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Types of Information Numeric (numbers) (integer/whole) (real/decimal) String (text) "Hello there!" "BOO" Pictures (numbers) Sound (numbers)
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AddNum problem The + operator works with: Text input boxes store text:
numbers, and text "23" + "16" "2316" double quotes enclose text Text input boxes store text: txtNum1.value + txtNum2.value We need to convert text to numbers
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String Functions parseInt("63") convert to integer result is 63 String("cat").charAt(0) result is "c" String("hello there!").slice(4,7) result is "o t" String("hello there!").substr(4,7) result is "o there" String("S Smith").length result is 7
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The Empty String Two double quotes (no space between)
"" Used to clear contents: txtNum.value = "";
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String Expressions
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Questions: String Expressions
What is the result of: String("what is the time?").substr(3, 4) What is the result of: String("bob sal").slice(2,6) Write an expression to: convert "16" to a number Write an expression to: give the first two letters of "Mr Jon Smith" "t is" "b sa" parseInt("16") String("Mr Jon Smith").substr(0, 2)
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String Expressions same pattern as numeric expressions:
"What is " + txtN1.value + " times " data operator
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String Expressions & Errors
"What is twice " txtN1.value + "?" "What is 6 minus " txtN1.value + "?" "This is a number + txtN1.value ERROR! missing operator ERROR! missing data ERROR! missing "
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Example: AddNum v2 parseInt converts to Integer <html>
<head><title>Add Numbers</title></head> <body> <input id="txtNum1" type="text" /><br /> <input id="txtNum2" type="text" /><br /> <input id="btnAdd" type="button" value="Add" onclick="btnAdd_onClick()"/> <p id="parResult"></p> </body> </html> <script language="javascript"> function btnAdd_onClick(){ parResult.innerText = parseInt(txtNum1.value) + parseInt(txtNum2.value); } </script> parseInt converts to Integer
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Error Types 3 error types :
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.
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Errors: Syntax Code cannot be understood
missing ( syntax error Browsers often ignore code with errors
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Errors: Run time Code cannot be executed Computer
missing e run time error Computer just symbol matching No intelligence
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Errors: Logical Code does not do what you wanted blue instead of red
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Questions: Errors Spot the errors (you should find 6), and
<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> Spot the errors (you should find 6), and decide whether they are syntax or logical JavaScript is case sensitive
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Debugging key skill: first step typical pattern in early tutorials:
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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Debugging Process What happens when run? Nothing?
Errors (syntax, or run-time)? Does the wrong thing (logical error)?
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Debugging Process murder investigation doctor treating patient
who-done-it? doctor treating patient diagnosis treatment scientific: observation experimentation (systematic)
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Example: Drinks SPECIFICATION User Requirements Software 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
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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
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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="spnBottlePrice"></span> per bottle<br /> £<span id="spnPintPrice"></span> per pint<br /> </body> </html> <script language="javascript"> function Calc_onClick(){ spnBottlePrice.innerText = txtQty.valu / txtPrice.value; spnPintPrice.innerText = spnBottlePrice.innerText * (568 / txtBottleSize.value); } </script>
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Debugging: Error Messages
Always read message Always click Break (this means pause)
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Debugging – Stop Button
Click Stop button, to edit code
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Debugging Clicking button gives NaN (Not a Number)
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Debugging: Breakpoints
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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Debugging: Breakpoints
Examine code line by line can help, but time consuming Breakpoint (press F9 on keyboard):
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Debugging: Breakpoint hit
After event-handler fixed breakpoint hit, code paused
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Debugging: Immediate Window
Use ? to ask ‘what is in txtQty.valu’ F8 run single line
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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 therefore: bottle price must be wrong
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Remarks Comments – ignored by computer: // JS uses 2 slashes for comments. function btnClear_onClick(){ txtNum1.Value = 0; // put 0 into txtNum1 } useful for: learning (you can explain your code) giving additional information (professional) disable line (rather than delete it)
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Tutorial Exercises: Temperature
LEARNING OBJECTIVE: to assign a value to an 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: AddNum
LEARNING OBJECTIVE: use a function to convert string (text) to integer (number) data Task 1: get the addnum examples (v1 and v2) working
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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: Student Loan
LEARNING OBJECTIVE: implement an algorithm in code Task 1: Create the user interface (page design) for the Student Loan example (from the lecture), using HTML tags (you will need a text box, a button, and a paragraph). Task 2: Add code that implements the following algorithm: When the Calculate button is clicked: read annual salary text box deduct £21000 calculate 9% put result in paragraph Task 3: Modify your program so that it calculates and displays monthly income and repayment amounts (as well an annual).
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