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04 – Information Processing: Expressions, Operators & Functions. 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

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04 information processing expressions operators functions
04 – Information Processing:Expressions, Operators & Functions


Session aims objectives
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
Information Processing

Input Data

Process

Output Data

7

*

63

9

  • All computing problems:

    • involve processinginformation/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


Information processing cont
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
Example: Multiply

txtNum1

lblResult

txtNum2

btnMultiply

Option Explicit

Private Sub btnMultiply_Click()

lblResult.Caption = txtNum1.Text * txtNum2.Text

End Sub


Expressions
Expressions

  • The following assignmentstatement:lblResult.Caption = txtNum1.Text * txtNum2.Text contains an expression

  • Given: 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)



Operators
Operators

  • Sit between the data5 + 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.Text * txtNum2.Text


Symbolic representation
Symbolic Representation

  • Symbols (names) representing data

    txtNum1.Text = "33"

  • Key concept in programming

Puts 33 into txtNum1.TextThe symbol txtNum1.Text

now represents 33


Numeric expressions
Numeric Expressions

many people instinctivelyknow these are wrong

data

data

data

data

  • 23 + 11 - txtNum1.Text * 2

  • 34 + * 12 + txtNum1.Text d o o d o d

  • txtNum1.Text + 1 – 21 45 d o d o d d

operator

operator

operator


String expressions
String Expressions

data

data

data

data

operator

operator

operator

  • "What is " & num1 & " times " & num2

  • "What is twice " num1 & "?"

  • "What is 6 minus " & & num & "?"

ERROR! missing operator

ERROR! missing data


Example addnum v1
Example: AddNum v1

txtNum1

lblResult

txtNum2

btnAdd

Option Explicit

Private Sub btnAdd_Click()

lblResult.Caption = txtNum1.Text + txtNum2.Text

End Sub


Types of information
Types of Information

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

  • Text (string) "Hello there!" "BOO"

  • Pictures

  • Sound


Addnum problem
AddNum problem

  • The + operator works with:

    • numbers, and

    • text

  • Double Quotes " used in VB to show literal text

  • Text input boxes store text

23 + 16 = 39

"23" + "16" = "2316"


Functions operators
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)

Function

Parameter(s)

Result

SQR

(16)

4


Functions cont
Functions (cont.)

  • Functions: come before the data (which is in brackets)Sqr(16) square root result is 4Abs(-23) absolute value result is 23Int(2.543) integer result is 2CInt("63") integer convert result is 63Left("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
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
Example: AddNum v2

Option Explicit

Private Sub btnAdd_Click()

lblResult.Caption = CInt(txtNum1.Text) + CInt(txtNum2.Text)

End Sub


Tutorial exercises
Tutorial Exercises

  • Task 1: get the multiply example (from the lecture) working

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

  • Task 3: create a project 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 DollarsGo on-line and look up the current exchange rate

  • Task 5: modify your currency converter, so that the result is displayed to 2 decimal places, e.g. $62.45(you will need to use the Format function, look it up in the help system for an explanation)

  • Task 6: modify your currency converter, replace the dollar label with a text box, and add another button that converts the dollar value back to pounds.

  • Task 7: modify your currency converter, so that when the user types into the pounds text box only the appropriate button is enabled.


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