05 – Problem Solving & Data Types

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# 05 – Problem Solving & Data Types - PowerPoint PPT Presentation

05 – Problem Solving & Data Types. Questions: Expressions. What is the result of: 10 * Int(3.1973265765) How many functions are in the following: Int(12.472) * Sqr(9) + 8 / 2 How many operators are in the following: Int(12.472) * Sqr(9) + 8 / 2

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## 05 – Problem Solving & Data Types

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Questions: Expressions
• What is the result of: 10 * Int(3.1973265765)
• How many functions are in the following:Int(12.472) * Sqr(9) + 8 / 2
• How many operators are in the following:Int(12.472) * Sqr(9) + 8 / 2
• Write an expression to: divide 15 by 3 and multiply the result by 6

30

2

3

(15 / 3) * 6

Can't touch this
• Student work from last week:

based on work done by Daniel Thornton & David Orrock

Questions
• name: event, object, property, eventhandler, operator, function, expression

<script language="vbscript">

imgHammer.style.posLeft = 500

imgHammer.style.posTop = 100

imgHammer.style.height = 100

imgHammer.style.width = 75

sndPlayer.URL = "Hammer.wav"

End Sub

Sub imgHammer_onMouseOver()

imgHammer.style.posLeft = Rnd() * (document.body.clientWidth - imgHammer.width)

imgHammer.style.posTop = Rnd() * (document.body.clientHeight - imgHammer.height)

End Sub

</script>

Session Aims & Objectives
• Aims
• to introduce the idea of types of data
• to provide a more explicit understanding of problem solving skills and strategies
• Objectives,by end of this week’s sessions, you should be able to:
• recognise different types of data
• numeric
• string (text)
• correct errors relating to data types
• recognise the key aspects of a problem
• start state
• goal state
• operations
• be able to use typical strategies to solve unfamiliar programming problems

<html>

<body>

<input type="text" id="txtNum1" /><br />

<input type="text" id="txtNum2" /><br />

<p id="lblResult"></p>

</body>

</html>

<script language="vbscript">

lblResult.innerText = txtNum1.value + txtNum2.value

End Sub

</script>

Doesn't work!

Types of Information
• Numeric (numbers) 29 (integer/whole) 56.23 (real/decimal)
• String (text) "Hello there!" "BOO"
• Pictures (numbers)
• Sound (numbers)

double quotes enclose text

• The + operator works with:
• numbers, and
• text

23 + 16 39

"23" + "16" "2316"

• Text input boxes store text:

txtNum1.value + txtNum2.value

• We need to convert text to numbers
String Functions

CInt("63") convert to integer result is 63Left("boo",2) left string result is "bo"Right("hello",3) right string result is "llo"Mid("hello",2,3) middle string result is "ell"Len("S Smith") length result is 7Space(5) spaces result is " "

String Expressions & Errors

data

data

data

operator

operator

ERROR! missing operator

ERROR! missing data

"What is " & txtN1.value & " times "

"What is twice " txtN1.value & "?"

"What is 6 minus " & & txtN1.value & "?"

"This is a number & txtN1.value

ERROR! missing "

Questions: String Expressions
• What is the result of:Mid("what is the time?", 3, 4)
• What is the result of: Left("bob", 2) & Right("sal", 1)
• Write an expression to:convert "16" to a number
• Write an expression to:give the first two letters of "Mr John Smith"

"at i"

"bol"

CInt("16")

Left("Mr John Smith", 2)

<html>

<body>

<input id="txtNum1" type="text" /><br />

<input id="txtNum2" type="text" /><br />

<p id="lblResult"></p>

</body>

</html>

<script language="vbscript">

lblResult.innerText = CInt(txtNum1.value) + CInt(txtNum2.value)

End Sub

</script>

Nested functions
• nested functions (one inside another): Right(Left("Hello there", 5), 2)
• do what is in the brackets first Right(Left("Hello there", 5), 2)= Right( "Hello" , 2)= "lo"
Types of problem
• two types of problem:
• Known problems:which we have successfully dealt with before, and can remember the solution
• Unknown problems:which we have never seen before, andtherefore have to discover / invent a solution for ourselves
What is a problem?
• All problems different
• However, have key parts:
• Start state
• Goal state
• set of available operations
• Problem solving is the process of searching for a sequence of operations that will take us from the start state to the goal state
Example: Light
• Start state: light is off
• Goal state: light on
• Set of operations:
• Push switch up (turns light on)
• Push switch down (turns light off)
• Solution:

1. Push switch up

Simple problems – small number of operations to solve

Important steps
• It is essential to understand the problem (start state, goal state, and operations) prior to finding a solution
• It is also often essential to be able to break a problem down into smaller sub-problems, i.e. identify intermediate sub-goal states
• failure to solve a problem is often due to these
More Complex Problems
• More complicated problems involve
• the use of multiple operations to get from the start to the goal state
• conditional execution of operations only do this if… (future lecture)
• repeated operations do this until… (future lecture)
• abstraction – more general description
Example: Horizontal mid point
• Start state: an image on the screen
• Goal state: to calculate its horizontal mid point
• Set of operations:
• posLeft: gives the position of its left edge
• posTop: gives the position of its top edge
• Width: gives the distance between its left and right edges
• Height: gives the distance between it top and bottom edges
• Solution:

1. get the posLeft value

Example: First Character
• Start state: the piece of text (e.g. "Hello")
• Goal state: extract the first character of a piece of text
• Set of operations:
• Len(s): gives the number of characters in s
• Right(s, n): gives n characters from the right of s
• Left(s, n): gives n characters from the left of s
• Mid(s, p, n): gives n characters from s, starting at position p
• Solution:

1. Left(text, 1)

Example: Movement
• Goal state
• Start state
• Operations
• Move Up
• Move Down
• Move Left
• Move Right
• Solution:
• Move Up
• Move Up
• Move Up
• Move Right
• Move Right
• Move Right
• Move Up
• Move Right
• Move Up
• Move Right
• Move Up
• Move Right

or

Concrete vs. Abstract problems
• People can solve concrete problems easily
• what is the first letter of hello
• what is the first letter of you surname
• an object's left edge is at position 100the object is 50 widewhere is its mid point?
• It is often difficult for them to describe the general (abstract) process they use
Concrete vs. Abstract code
• we have:
• posLeft
• posTop
• right = left + width
• middle = left + (width / 2)
• concrete code (works for window 800px wide): picBall.style.posLeft = 400
• vs. abstract code (works for all window widths): picBall.style.posLeft = document.body.clientWidth / 2
Humans vs. Computers
• Humans and Computers work very differently
• Humans
• declarative (goals): flexible sequence
• instinctive (without conscious thinking)
• easily deal with incomplete and incorrect data
• error prone (especially mundane repetitive tasks)
• Computers
• procedural / algorithmic: fixed sequence
• do exactly what they are told
• cannot deal with errors
• no imagination or creativity
Algorithms
• algorithm: step-by-step sequence of instructions, to solve a problem
• it describes how input data is to be processed in order to produce a desired output
• similar to recipe
• ingredients (similar to data)
• method (is a type of algorithm)
Algorithms
• Making a cup of tea:

1. Fill the kettle with water

2. Plug the kettle in

3. Switch the kettle on

4. Wait for the kettle to boil

5. Put water in cup

6. Put a tea bag into the cup

7. Add sugar to the cup

8. Add milk to the cup

9. Stir

10. Take the tea bag out

What vs. How
• what vs. how:
• What: increase value of a text box by 1
• How:
• put the result back in the text box
• For example: swap, search, sort
Example: Swap v1
• put txtB into txtA
• put txtA into txtB

<html>

<body>

<input id="txtA" type="text" value="Bob" />

<input id="txtB" type="text" value="Sally" />

<input id="btnSwap" type="button" value="Swap" />

</body>

</html>

<script language="vbscript">

Sub btnSwap_onClick()

txtA.value = txtB.value

txtB.value = txtA.value

End Sub

</script>

• does not work!
Example: Swap v2

<html>

<body>

<input id="txtA" type="text" value="Bob" />

<input id="txtB" type="text" value="Sally" />

<input id="btnSwap" type="button" value="Swap" />

<input id="txtTemp" type="text" disabled="disabled" />

</body>

</html>

<script language="vbscript">

Sub btnSwap_onClick()

txtTemp.value = txtA.value

txtA.value = txtB.value

txtB.value = txtTemp.value

End Sub

</script>

• put txtA into temp
• put txtB into txtA
• put temp into txtB
• works!
The Empty String
• Two double quotes (no space between)

""

• Used to clear contents:

txtNum.value = ""

Example: Student Loan (Analysis)
• What: Calculate annual student load repayment from salary
• How:
• Algorithm:
• deduct £15000
• calculate 9%
• display result
Example: Student Loan (Design)
• When Calculate button is clicked:
• read annual salary text box
• deduct £15000
• calculate 9%
• put result in paragraph
• Test Data:

Input Process Output

• £15000 15000-15000*0.09 = £0
• £16000 16000-15000*0.09 = £90
Generating Assignment Code
• put "Hello" into txtAtxtA.value = "Hello"
• get txtA and join it with txtB, and put the result in parResparRes.innerText = txtA.value + txtB.value
• put into txtNum2, the result of multiplying txtNum1 by 2txtNum2.innerText = txtNum1.value * 2
Questions: Assignment
• What is the code for:
• put 0 into the posLeft property of picHouse
• increase the posTop property of picHouse by 5
• decrease the posTop property of picCar by 9

picHouse.style.posLeft = 0

picHouse.style.posTop = picHouse.style.posTop + 5

picCar.style.posTop = picCar.style.posTop - 9

Errors
• txtTemp.value = "" + 5 type mismatch (cannot add "" to 5)
• txtTemp.value = "7" + 5 OK – VB converts "7" into 7 automatically
• txtTemp.value = 7 + 5 OK – 7 plus 5 is 12
• value.txtTemp = 7 + 5 object required 'value' (object comes first)
Example: Text Shift

<html>

<body>

<p id="parH"></p>

</body>

</html>

<script language="vbscript">

parH.innerText = "Hello There" & Space(100)

window.setInterval "TextShift()", 50

End Sub

Sub TextShift()

parH.innerText = Mid(parH.innerText,2) & Left(parH.innerText,1)

End Sub

</script>

• LEARNING OBJECTIVE:use a function to convert string (text) to integer (number) data
Tutorial Exercises: Swap
• LEARNING OBJECTIVE:use an algorithm to solve a problem
• Task 1: get the swap examples (v1 and v2) working
• Task 2: change v2 of the swap page so that the temporary text box is hidden
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 £15000
• 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).
Tutorial Exercises: Text Shift
• LEARNING OBJECTIVE:develop and implement an algorithm to solve a problemuse string manipulation functions, and sound
• Task 1: get the Text Shift example (from the lecture) working
• Task 2: modify your program so that the text goes the other way.
• Task 3: modify your program so that a noise is made when the user moves the mouse over the text.