04 – information processing: expressions, operators & functions

Mark Dixon, SoCCE SOFT 131

04 – Information Processing:Expressions, Operators & Functions


Questions: Events

• Consider the following code:

a) How many unique events does it contain?

b) Name the event(s).

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 IfEnd Sub

1

ClickOnClick


Questions: Properties


a) How many unique properties does it contain?

b) Name the properties.


3

value, bgcolor, & innertext


Questions: Keywords


a) How many unique keywords does it contain?

b) Name the keywords.


5

Sub, If, Then, Else, & End


Session Aims & Objectives• Aims

– 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:

– evaluate expressions– assign a value to a object's property,

• using combination of literal values, operators, functions, and identifiers


Information Processing• All computing problems:

– involve processing information/data• information has meaning (e.g. 5lb 3.3kg 18 years)• data has no meaning (e.g 5 3.3 18)

– following this pattern:

• For example:– to multiply two numbers: 7 * 9 = 63

Input Data Process Output Data

9

763*


Information Processing (cont.)• Hence, to solve any computing problem ask:

– what information goes in

– what processing is done to it

– what information comes out


Example: Multiply<html> <head> <title></title> <script language="VBScript"> Sub btnMultiply_OnClick() lblResult.InnerText = txtNum1.Value * txtNum2.Value End Sub </script> </head> <body> <input type="text" ID=txtNum1> <input type="text" ID=txtNum2> <input type="button" ID=btnMultiply value="Multiply"> <p ID=lblResult> </body></html>


Operators• Sit between the data

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 "5" & "2" string concatenation result is "52"

• work with objects: txtNum1.Value * txtNum2.Value


• The following assignment statement:lblResult.InnerText = txtNum1.Value * txtNum2.Value

contains an expression

Expressions

• Given: txtNum1.Value = "7", txtNum2.Value = "9"can evaluate expression:lblResult.InnerText = txtNum1.Value * txtNum2.Value

(from above)lblResult.InnerText = "7" * "9" (substitute)lblResult.InnerText = 63 (calculate)Animation


Example: AddNum v1<html> <head> <title></title> <script language="VBScript"> Sub btnAdd_OnClick() lblResult.InnerText = txtNum1.Value + txtNum2.Value End Sub </script> </head> <body> <input type="text" ID=txtNum1> <input type="text" ID=txtNum2> <input type="button" ID=btnAdd value="Add"> <p ID=lblResult> </body></html>


Types of Information• Numbers (numeric) 29 (integer/whole) 56.23 (decimal/real)

• Text (string) "Hello there!""BOO"

• Pictures

• Sound


AddNum problem

• The + operator works with:– numbers, and

– text

• Text input boxes store text

23 + 16 = 39

"23" + "16" = "2316"


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

SQR

Function

(16) 4


Functions (cont.)• Functions: come before the data (which is in

brackets) Sqr(16) square root result is 4 Abs(-23) absolute value result is 23 Int(2.543) integer result is 2 CInt("63") integer convert result is 63 Left("boo",2) left string result is "bo" Right("hello",3) right string result is "llo" Mid("hello",2,2) middle string result is "el"


Questions: Expressions• What is the result of:

1 + CInt("23") + Int(2.76786) + Sqr(Int(9.4523))

• What is the result of:

"23" & "18" + Left("bob",1) + Right("sal",2)

• Write an expression to:

give integer value of "16.7658765"

• Write an expression to:

give the first two letters of "Mr John Smith"

1 + 23 + 2 + 3 = 29

"23" & "18" & "b" & "al" = "2318bal"

Int(CInt("16.7658765"))

Left("Mr John Smith", 2)


Example: AddNum v2<html> <head> <title></title> <script language="VBScript"> Sub btnAdd_OnClick() lblResult.InnerText = CInt(txtNum1.Value) + CInt(txtNum2.Value) End Sub </script> </head> <body> <input type="text" ID=txtNum1> <input type="text" ID=txtNum2> <input type="button" ID=btnAdd value="Add"> <p ID=lblResult> </body></html>


Testing & Debugging: Errors• 3 error types :

– syntax: computer unable to understand your instructions (program does not execute), e.g.

• variable not defined (probably most common)

– run-time: program can't execute instruction and exits (future lecture)

• Device unavailable (e.g. floppy drive)

– logical: program executes but does not not match specification (do what was intended), e.g.

• clicking on button does nothing, when you thought you attached code to it

• clicking on blue button changes colour to red (when it should change to blue)


<html> <head> <title>Hello</title> <script language="VBScript"> Sub btnHello_OnCluck() lblHello.inerText = "Hello" End Sub </script> </head> <body> <input type=button ID=btnHello Value="Hello"> <p ID=lblHello> </body></html>

• Computer – just symbol matching– No intelligence

Example: Hello Errors

missing nn: syntax error

u instead of i: logical error (button does nothing)


Questions: Errors

• The following example is from lecture 1,– Spot the errors (you

should find 6), and– decide whether they are

syntax or logical

<html> <head> <title>Hello</title> <script language="VBScript"> Sub btnBlue_OnCluck() document.bgColor = "Red" End Sub Sub btnRed_Onlick() document.bgColor "Red" End Sub Sub window_OnClick() document.bgColour = "White" End Sib </script> </head> <body> <input type=button ID=btnRed Value="Red"> <input type=button ID=btnBlue Value="Blue"> <p ID=lblHello> </body></html>


Tutorial Exercises

• Task 1: get multiple example working

• Task 2: get addnum examples (v1 and v2) working

• Task 3: create a new page with two text boxes (surname and forenames), and a button (initials). When the button is clicked the first character from each text box (i.e. the person's initials) should be displayed.

• Task 4: create a new page that helps the user covert from Pounds to Dollars

04 – information processing: expressions, operators & functions

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