04 – Information Processing: Expressions, Operators &amp; Functions

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

04 – Information Processing: Expressions, Operators &amp; Functions. Session Aims &amp; 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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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

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 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)

Option Explicit