Mark Dixon, SoCCE SOFT 131Page 1 04 – Information Processing: Expressions, Operators & Functions

Mark Dixon, SoCCE SOFT 131Page 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

Mark Dixon, SoCCE SOFT 131Page 3 Information Processing All computing problems: –involve processing information/data information has meaning (e.g. 5lb 3.3kg 18 years) data has no meaning (e.g ) –following this pattern: For example: –to multiply two numbers: 7 * 9 = 63 Input DataProcessOutput Data *

Mark Dixon, SoCCE SOFT 131Page 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

Mark Dixon, SoCCE SOFT 131Page 5 Example: Multiply Option Explicit Private Sub btnMultiply_Click() lblResult.Caption = txtNum1.Text * txtNum2.Text End Sub lblResult btnMultiply txtNum1 txtNum2

Mark Dixon, SoCCE SOFT 131Page 6 The following assignment statement: lblResult.Caption = txtNum1.Text * txtNum2.Text contains an expression Expressions 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)

Mark Dixon, SoCCE SOFT 131Page 7 Expression Evaluation

Mark Dixon, SoCCE SOFT 131Page 8 Operators Sit between the data addition operatorresult is 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

Mark Dixon, SoCCE SOFT 131Page 9 Symbolic Representation Symbols (names) representing data txtNum1.Text = "33" Key concept in programming Puts 33 into txtNum1.Text The symbol txtNum1.Text now represents 33

Mark Dixon, SoCCE SOFT 131Page 10 Numeric Expressions txtNum1.Text * * 12 + txtNum1.Text d o o d o d txtNum1.Text + 1 – d o d o d d many people instinctively know these are wrong data operator data operator

Mark Dixon, SoCCE SOFT 131Page 11 String Expressions "What is " & num1 & " times " & num2 "What is twice " num1 & "?" "What is 6 minus " & & num & "?" data operator data operator ERROR! missing data ERROR! missing operator

Mark Dixon, SoCCE SOFT 131Page 12 Example: AddNum v1 Option Explicit Private Sub btnAdd_Click() lblResult.Caption = txtNum1.Text + txtNum2.Text End Sub lblResult btnAdd txtNum1 txtNum2

Mark Dixon, SoCCE SOFT 131Page 13 Types of Information Numbers (numeric)29 (integer/whole) (decimal/real) Text (string)"Hello there!" "BOO" Pictures Sound

Mark Dixon, SoCCE SOFT 131Page 14 AddNum problem The + operator works with: –numbers, and –text Double Quotes " used in VB to show literal text Text input boxes store text = 39 "23" + "16" = "2316"

Mark Dixon, SoCCE SOFT 131Page 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) Parameter(s) Result SQR Function (16)4

Mark Dixon, SoCCE SOFT 131Page 16 Functions (cont.) Functions: come before the data (which is in brackets) Sqr(16) square rootresult is 4 Abs(-23) absolute valueresult is 23 Int(2.543) integerresult is 2 CInt("63") integer convertresult is 63 Left("boo",2) left stringresult is "bo" Right("hello",3) right stringresult is "llo" Mid("hello",2,2) middle stringresult is "el"

Mark Dixon, SoCCE SOFT 131Page 17 Questions: Expressions What is the result of: 1 + CInt("23") + Int( ) + 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 " " Write an expression to: give the first two letters of "Mr John Smith" = 29 "23" & "18" & "b" & "al" = "2318bal" Int(CInt(" ")) Left("Mr John Smith", 2)

Mark Dixon, SoCCE SOFT 131Page 18 Example: AddNum v2 Option Explicit Private Sub btnAdd_Click() lblResult.Caption = CInt( txtNum1.Text ) + CInt( txtNum2.Text ) End Sub

Mark Dixon, SoCCE SOFT 131Page 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 Dollars Go 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.