# 04 – Information Processing: Expressions, Operators & Functions - PowerPoint PPT Presentation

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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

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### 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

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.)

• Hence, to solve any computing problem ask:

• what information goes in

• what processing is done to it

• what information comes out

### Example: Multiply

txtNum1

lblResult

txtNum2

btnMultiply

Option Explicit

Private Sub btnMultiply_Click()

lblResult.Caption = txtNum1.Text * txtNum2.Text

End Sub

### Expressions

• The following assignmentstatement:lblResult.Caption = txtNum1.Text * txtNum2.Textcontains 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

• Sit between the data5 + 2 addition operatorresult is 7 5 - 2 subtraction operatorresult is 3 5 * 2 multiplication operatorresult is 10 5 / 2 division operatorresult is 2.5 "5" & "2" string concatenationresult is "52"

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

### 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

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

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

txtNum1

lblResult

txtNum2

Option Explicit

lblResult.Caption = txtNum1.Text + txtNum2.Text

End Sub

### Types of Information

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

• Text (string)"Hello there!""BOO"

• Pictures

• Sound

• 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

• 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: come before the data (which is in brackets)Sqr(16) square rootresult is 4Abs(-23) absolute valueresult is 23Int(2.543) integerresult is 2CInt("63") integer convertresult is 63Left("boo",2) left stringresult is "bo"Right("hello",3) right stringresult is "llo"Mid("hello",2,2) middle stringresult 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)

Option Explicit

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

End Sub

### 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.