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04 – Information Processing: Expressions, Operators & Functions

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Presentation Transcript

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.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

- 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

- 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

Example: AddNum v1

txtNum1

lblResult

txtNum2

btnAdd

Option Explicit

Private Sub btnAdd_Click()

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

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

- 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 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

- 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

Option Explicit

Private Sub btnAdd_Click()

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.

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