1. ‘Tirgul’ # 2 Enterprise Development Using Visual Basic 6.0 Autumn 2002 Tirgul #2

2. ‘Tirgul’ # 2 Short Quiz What is a property? What is the difference between Sub and Function? Write a sub that gets 2 integers and perform an Add operation Write the same as function

3. ‘Tirgul’ # 2 Objective Variables types In a nutshell –If - Then - Else –Case –Loops Write general sub procedures Write user-defined functions Examine some String manipulations

4. ‘Tirgul’ # 2 Declaring Variables Private, public – In a general module Dim (Inside a sub/form) –New memory location to a variable Static(Inside a sub/form) –retains its value between procedure calls –uses same memory location and keeps old value –Use static for variables whose values are persistent (totals, counts, etc.) Const – for constants Sub test() static i As Integer i= i + 1 End Sub Sub test() dim i As Integer i= i + 1 End Sub

5. ‘Tirgul’ # 2 Declaring Variables 2 dim counter As Integer private middleName As String Static Index as Integer Public const ARRAY_SIZE= 10

6. ‘Tirgul’ # 2 Declaring Variables 3 Data Types –Boolean - True or false –Date - From Jan 1, 100 to Dec 31, 9999 –Integer - Numbers without a decimal point –Long - Long integer –Single - Numbers with a decimal point –Double - Long Single –Currency - Dollar amounts –String - Character and alphanumeric data –Object - Any object reference such as Word document –Variant - default, can hold any data type

7. ‘Tirgul’ # 2 Data conversion Int to String? Use STR String to Int? Use Cint String to Numeric? Use Val – (Generic) Str(num) Cint(Str) Val(Str)

8. ‘Tirgul’ # 2 Decisions in VB Used to alter the flow of a program while program is running based on TRUE/FALSE If condition Then statements to be executed if condition is true End If

9. ‘Tirgul’ # 2 Decisions in VB 2 Complementary condition Use Else to perform both cases If condition Then statements to be executed if condition is TRUE Else statements to be executed if condition is FALSE If

10. ‘Tirgul’ # 2 Example If index > 10 Then print “Index > 10” End If If index > 10 Then print “Index > 10” Else print ? End If

11. ‘Tirgul’ # 2 Indentation!!! Indentation!!! I rest my case…

12. ‘Tirgul’ # 2 More IF Examples If index > 10 AND printFlag = true Then print “Index > 10” End If If index > 10 OR printFlag = true Then print ? End If

13. ‘Tirgul’ # 2 Using IF in actual VB programming TRUE FALSE

14. ‘Tirgul’ # 2 Code: If opt1.Value = True Then print “Option 1 selected” End If If opt1.Value = Checked Then print “Option 1 selected” Else print “Option 2 selected” End If

15. ‘Tirgul’ # 2 Case Structure Case Can replaces IF Code readability – Important issue! valueList options –Case 1 –Case 2 to 5 –Case 6, 9 –Case Is >= 10 –Case “text”

16. ‘Tirgul’ # 2 Example Select Case textValue Case “Print” print Case “send” sendMail Case Else defaultAction End Select

17. ‘Tirgul’ # 2 Loops The group of repeated instructions is called a loop a single execution of the statements in the loop is called an iteration All loops must have a mechanism to control the number of iterations Breaking point!

18. ‘Tirgul’ # 2 For / Next Loops Format: For loopIndex = initialValue to testValue [Step increment] body of loop Next loopIndex Items enclosed in [ ] are optional loopIndex index is declared before loopIndex must be a numeric variable, testValue may be any numeric expression (e.g. function) Use For when you know the number of iterations.

19. ‘Tirgul’ # 2 Example Dim index as integer For index = 1 to 10 print index Next index

20. ‘Tirgul’ # 2 Procedures Event procedures - –associated with control events –bounded by Sub and End Sub General procedures - –not associated with events –consist of statements that are grouped together because they perform a specific task

21. ‘Tirgul’ # 2 Example Event Procedures Private Sub cmdExit_Click() closeConnection End Sub Private Sub cmdDisplay_Click() refreshData End Sub Private Sub Form_Load() openConnection End Sub

22. ‘Tirgul’ # 2 General procedures written in the General code section, but in a different window from the declarations two types: –Sub procedure - performs an action –Function procedure - performs an action and returns a value. Format is based on mathematical notation: f(x), g(x, y) May be user-defined or built in to VB (intrinsic)

23. ‘Tirgul’ # 2 VB Intrinsic Functions Operate on 0 or more variables, and return exactly 1 value Functions we have already used: –Val(numeric string) returns a numeric value –Format(number, format string) returns a string in a specific form –Conversion functions Review

24. ‘Tirgul’ # 2 More intrinsic functions General math –sqr( ), abs( ), exp( ), log( ), rnd( ) Trigonometric functions –sin( ), cos( ), tan( ) Financial functions String Functions Review

25. ‘Tirgul’ # 2 String Functions Len - returns the length of a string Left, Mid, Right - returns the left, right, or middle part of a string Instr - returns the position of one string within another, or 0 if not found also note that “+” or “&” concatenates 2 strings together Review

26. ‘Tirgul’ # 2 Example 1 Sub procedure PrintMessage is called from within the Click event procedure No arguments Private Sub PrintMessage( ) Print “Hello” End Sub Private Sub cmdDisplay_Click( ) PrintMessage End Sub

27. ‘Tirgul’ # 2 Example 2 Sub procedure Add_And_Print is called from within the Click event procedure Two arguments - Score1 and Score2 Sub Add_And_Print (x as Single, y as Single) picOut.Print x + y End Sub Private Sub cmdDisplay_Click( ) Add_And_Print (Score1, Score2) End Sub

28. ‘Tirgul’ # 2 Parameter passing When variables are used as inputs (parameters) –Parameters type must be consistent –order of Parameters –Optional - [ ] Sub Output (stName as String, iNum as Integer) Print stName, iNum End Sub ‘in another Sub Call Output (“Joe”, 31) ‘ NOT Call Output(31, “Joe”) Call Output (stFirst, sAge)

29. ‘Tirgul’ # 2 User Defined Functions starts with the word FUNCTION returns EXACTLY ONE value - as a given type called by using its name on the right side of an assignment statement, returns to a variable on the left side of an assignment statement Function Add_Two (x as Integer, y as Integer) as Integer Add_Two = x + y End Function ‘ in calling sub sum = Add_Two(5, 6)

30. ‘Tirgul’ # 2 Sample Functions Function NewName (stFirst as String, stSec as String) as String NewName = stFirst + “ “ + stSec End Function Function Celsius (ByVal fahrentemp As Single) as Single Celsius = 5/9*(fahrentemp - 32) End Function

31. ‘Tirgul’ # 2 Example Find whatever a given integer is a perfect number.

32. ‘Tirgul’ # 2 Example(2) Factorial Example Factorial(10) ?

33. ‘Tirgul’ # 2 String Manipulation Usefull String manipulations: str = “welcome mid(str,4,4) = ? (watch index!!!) str1 = “welcome” str2 = “come” InStr(1,str1,str2) = ?

34. ‘Tirgul’ # 2 String Manipulation (2) StrComp function return variant (Integer) indicating the result of a string comparison. Syntax : - StrComp(string1, string2, [compare]) dim MyStr1, MyStr2 As String dim MyComp As Integer MyComp = StrComp (MyStr1, MyStr2, vbDatabaseCompare) : returns 0 MyComp = StrComp (MyStr1, MyStr2, vbBinaryCompare) : Returns - 1 MyComp = StrComp (MyStr2, MyStr1) : Returns 1 0vbBinaryCompare - Performs a binary comparison. 1vbTextCompare Performs a textual comparison. 2vbDatabaseCompare For Microsoft Access performs a comparison based on information contained in your database.