mark dixon, socce soft 131page 1 05 – information processing: data-types, variables, operators...

Mark Dixon, SoCCE SOFT 131

05 – Information Processing:Data-types, Variables,Operators & Functions


Session Aims & Objectives• Aims

– Introduce you to data storage concepts, i.e. data types and variables

– Introduce you to processing concepts, i.e. operators and functions

• Objectives,by end of this week’s sessions, you should be able to:

– declare a variable, selecting appropriate data type– assign a value to a variable,

• 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

Option Explicit

Private Sub btnMultiply_Click() lblResult.Caption = txtNum1.Text * txtNum2.TextEnd Sub

Multiply


Expressions: Evaluation, & Substitution

• The following assignment statement: lblResult.Caption = txtNum1.Text * txtNum2.Text

contains an expression

• Given values for txtNum1.Text and txtNum2.Text

txtNum1.Text = "7", txtNum2.Text = "9"can evaluate expression: lblResult.Caption = txtNum1.Text * txtNum2.Text

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


Example: AddNum v1

Option Explicit

Private Sub btnAdd_Click() lblResult.Caption = txtNum1.Text + txtNum2.TextEnd Sub

AddNum


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)

FunctionParameter(s) Result


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

Sqr(16) square root function result is 4 Abs(-23) absolute value function result is 23 Int(2.543) integer function result is 2 Val("63") value function result is 63 Left$("123",2) left string function result is "12"

• 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"


Exercise: Expressions• What is the result of:

1 + Val("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(Val("16.7658765"))

Left$("Mr John Smith", 2)


Example: AddNum v2

Option Explicit

Private Sub btnAdd_Click() lblResult.Caption = Val(txtNum1.Text) + Val(txtNum2.Text)End Sub

AddNum


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

56.23 (decimal/real)

• Text “Hello there!” “BOO”

• Pictures

• Sound


Data Types• Integer – whole numbers

• Long – whole numbers (large)

• Single – decimal numbers

• Double – decimal numbers (more precise)

• Currency – money

• String – text


Data Type Selection

Will the numberever have afraction?

Will the numberever be large?

number

What informationwill it hold?

String

Long

Integer

text

yes

no yes

no

Currencymoney Will the number

ever need to bevery precise?

Double

Single

yes

no


Data Storage• Data can be stored in

– Controls• visible to user (although can use visible property to hide)

• take lots of memory

• slow to access

– Variables

• Not visible to user

• take up very little memory

• fast to access


Example: GuessNum - AnalysisSPECIFICATION

• User Requirements – need to keep children occupied/entertained, while

learning about maths

• Software Requirements– Functional:

–computer picks a number between 0 and 100–user enters a number–compare numbers and display appropriate

message– Non-functional

should be easy and fun to use


Variables (why?)• Variables useful for:

– reducing memory use

– speed up execution

– storing information you don't want user to see

– storing intermediate results of calculations temporarily (makes code easier to understand)

– making code easier to read (short variable name instead of long object.property names)


Variables (what)• Variables have

– Identifier (name) – you choose this, used to refer to (reference) variable

– Type – you choose this (to suit purpose)– Value – you set/change this

23x IntegerName/Identifier

Value TypeMemory


Variable declaration (how 1)• Variables must be declared,

using the following syntax (grammar):

Dim <identifier> As <type>

e.g. Dim weight As doubleDim x As longDim s As stringDim year As long


Exercise: Variable declaration

• Write a line of code that:

– Declares a variable called x of type double

– Declares a variable called y of type integer

– Declares a variable called surname of type string

– Declares a variable called age of type integer

Dim x As double

Dim y As integer

Dim surname As string

Dim age As integer


Variable assignment (how 2)• Variables are assigned values,

using the following syntax:

<identifier> = <expression>

e.g. x = 5 weight = 109.45name = "Bob" s = "Hello "

Note: the data flows backwards (from right to left)


Exercise: Variable assignment

• Write a line of code that:

– Assigns the value of 23 to the variable y

– Assigns the value of 14.6 to the variable x

– Assigns the value of ‘John’ to the variable surname

– Assigns the value of 21 to the variable age

y = 23

x = 14.6

surname = "John"

age = 21


Demo


Example: AddNum v3Private Sub btnAdd_Click()Dim num1 As DoubleDim num2 As DoubleDim res As Double num1 = Val(txtNum1.Text) num2 = Val(txtNum2.Text) res = num1 + num2 lblResult.Caption = resEnd Sub

AddNum

• Variables used to:– spread code over several lines– makes code easier to understand


Example: GuessNum - CodeOption ExplicitDim GuessNum As Long

Private Sub Form_Load() Randomize GuessNum = Rnd() * 100End Sub

Private Sub btnGuess_Click() If txtGuessNum.Text = GuessNum Then lblResult.Caption = "Correct" Else lblResult.Caption = "Wrong, please try again" End IfEnd Sub

txtGuessNum

btnGuess

lblResult


Variables: ErrorsOption ExplicitDim z as integer

Sub Form_Click ()Dim s As StringDim x As IntegerDim x As Integer Print y Print z x = 40000 x = "21" s = 21 x = 3.2End Sub

OK, forces explicit variable declarationOK

OKOKOK Duplicate definition error. Variable not defined error.OK, as z was declared at the form level. Overflow error. Type mismatch error. Type mismatch error.OK (however x will be 3).


Exercise: Variable assignment 2• Write a line of code that:

– Increases the value of x by 2.89

– Decreases the value of z by y

– Divides Km by 1.6 and puts the result in Miles

– Joins two strings Surname and Forenames together, putting the result in LongName

x = x + 2.89

z = z - y

Miles = Km / 1.6

LongName = Surname & Forenames

mark dixon, socce soft 131page 1 05 – information processing: data-types, variables, operators...

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