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04 – Information Processing: Expressions, Operators & Functions

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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  1. 04 – Information Processing:Expressions, Operators & Functions

  2. 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

  3. 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

  4. Information Processing (cont.) • Hence, to solve any computing problem ask: • what information goes in • what processing is done to it • what information comes out

  5. Example: Multiply txtNum1 lblResult txtNum2 btnMultiply Option Explicit Private Sub btnMultiply_Click() lblResult.Caption = txtNum1.Text * txtNum2.Text End Sub

  6. 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)

  7. Expression Evaluation

  8. 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

  9. Symbolic Representation • Symbols (names) representing data txtNum1.Text = "33" • Key concept in programming Puts 33 into txtNum1.TextThe symbol txtNum1.Text now represents 33

  10. 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

  11. 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

  12. Example: AddNum v1 txtNum1 lblResult txtNum2 btnAdd Option Explicit Private Sub btnAdd_Click() lblResult.Caption = txtNum1.Text + txtNum2.Text End Sub

  13. Types of Information • Numbers (numeric) 29 (integer/whole) 56.23 (decimal/real) • Text (string) "Hello there!" "BOO" • Pictures • Sound

  14. 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"

  15. 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

  16. 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"

  17. 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)

  18. Example: AddNum v2 Option Explicit Private Sub btnAdd_Click() lblResult.Caption = CInt(txtNum1.Text) + CInt(txtNum2.Text) End Sub

  19. 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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