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Mastering Visual Basic Control Structures: IF, ELSE, SELECT, Arrays, and Loops

Dive into essential concepts like IF-ELSE, SELECT CASE, Arrays, and Loops in Visual Basic programming. Understand decision-making, iterative control, and array management. Master manipulating data structures for efficient code execution.

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Mastering Visual Basic Control Structures: IF, ELSE, SELECT, Arrays, and Loops

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  1. Controlling Execution

  2. IF and only if.. • One line IF • IF with and without ENDIF • IF with and without ELSE • One line ELSEIF • Multiple ELSEIFs and Select Case

  3. IF and only if.. • One line IF (without END IF) IF (condition) Then Exit Sub • One seeming line IF IF (condition) Then _ Exit Sub • IF with ENDIF IF (condition) Then Exit Sub END IF

  4. IF and only if.. • One line IF with ELSE IF (whatever) Then Yada ELSE YadaYada • Five line IF with ELSE IF (whatever) Then Yada ELSE YadaYada END IF

  5. IF and only if.. • ELSE required alone on one line IF (whatever) Then Yada ELSE YadaYada END IF • THEN at end of line required • END IF required alone on one line

  6. ElseIF and only if.. • ElseIF is subordinate to the previous IF IF (whatever) Then Yada ElseIF (whatever) Then YadaYada ELSE YadaYadaYada END IF

  7. Select Case vs ElseIF • Select Case neat and maintainable • Case formats very flexible • Case 1,3,7 • Case 2 to 8 • Case “CA” to “NM” • Case Is > 21

  8. Select Case Example Select Case Security Case "V" ' set properties for volunteers Case "S" ' set properties for supervisors Case "" ' exit sub End Select

  9. Immediate If! • IIF is a function • IIF(condition, true return, false return) • IIF(blnMale=True,”Male”,”Female”) • Useful in queries, properties, division • IIF(intN > 0, 300/intN, 0) ' to avoid an error msg • IIF(PercentCorrect>=90,"A", _ • IIf(PercentCorrect>=80,"B", _ • IIf(PercentCorrect>=70,"C", _ • IIf(PercentCorrect>=60,"D","F"))))

  10. For Loops • For intX = 1 to 10 Step 2 • For Each varX in varDataSet • Next required for these two For formats • Exit For Restrictions on For Each… • 1-dimension only • Each control variable must be Variant

  11. For Loops: Examples Dim varDataSet(0 to 49) as Variant Dim intX as Integer, intOdd as Integer Dim intSum as Integer Dim varItem as Variant, varSum as Variant ' sum the odd numbered elements (1,3,5,…) For intX = 1 to 49 Step 2 intOdd = intOdd + varData(intX) Next ' sum all elements (1,2,3,…) For Each varItem in varDataSet intSum = intSum + varItem Next

  12. Do Loops Conditional logic after 1 pass through loop • Do … Loop While • Do … Loop Until Or, conditional logic before 1st pass through loop • Do While … Loop • Do Until … Loop Exit Do

  13. Arrays • Lists (states, income levels, schedules, etc) • Private, Public, fixed or dynamic size • Dim ccyIncomeLevel(0 to 5) As Currency

  14. Which Array to Go? • Option Base 1 or Option Base 0? • Public strState(0 to 49) As String • Public strState(1 to 50) As String • Public strState(50) As String • Above will be (0 to 49 or 1 to 50)depending on Option Base

  15. strMonth(1) = "January" strMonth(2) = "February" strMonth(3) = "March" strMonth(4) = "April" strMonth(5) = "May" intInput = InputBox("Enter Month Number") MsgBox “You mean “& strMonth(intInput) & “?” Or MsgBox “You mean “& strMonth(intInput+1) & “?”

  16. Flexible Array • Dynamic • Dim ccyLevel() As Currency • Expands and contracts • Good for uncertain run-time conditions • Can loose contents unless… • Redim Preserve ccyLevel(7) • Can erase dynamic arrays: Erase ccyLevel

  17. Strings

  18. Notes on strings • String variables (Dim strName as String) • String literals (txtName = "Jones") • Mixing variables and literals Select * from tblRoster Where Name = "Smith" • How to embed quotes around strName? "Select * from tblRoster Where Name =" & ???

  19. How to embed single quotes ' If the name is a hard-coded literal Debug.Print "Name = 'Smith'" ' If the name is in a variable (very likely) Dim strName As String strName = "Smith" Debug.Print "Name = '" & strName & "'"

  20. How to embed double quoteswith literal strings ' When the name is a hard-coded literal Debug.Print "LastName = ""Smith""" 'Coding hints for the triple quotes above: 'step 1: LastName = "Smith" 'step 2: LastName = ""Smith"" 'step 3: "LastName = ""Smith"" "

  21. How to embed double quotesusing variables Dim strName As String strName = "Smith" Debug.Print "LastName = """ & strName & """" 'Coding hints for triple/quadruple quotes: 'step 1: "LastName = strName" 'step 2: "LastName = """ & strName " 'step 3: "LastName = """ & strName & """ "

  22. How to embed double quotesas a variable Dim strName As String strName = "Nguyen" Dim strQuote As String strQuote = Chr(34) ' ACSII for double quote strName = strQuote & strName & strQuote Debug.Print "LastName = " &strName

  23. String Functions • mid(strHayStack, intStart, intLength) • Returns string or part of a string • instr(intStart, strHayStack, strNeedle) • Returns position where needle is in haystack

  24. Mid() MyString = "Mid Function Demo" ' Create text string. FirstWord = Mid(MyString, 1, 3) ' Returns "Mid". LastWord = Mid(MyString, 14, 4) ' Returns "Demo". MidWords = Mid(MyString, 5) ' Returns "Function Demo".

  25. InStr() strHaystack ="XXpXXpXXPXXP“ strNeedle = "p" intWhere = Instr(1, strHaystack , "W") Returns 0 intWhere = Instr(4, strHaystack , strNeedle ) Returns 6

  26. Other String Functions • Left() and Right() ' args: string, no. of chars • Ucase() and Lcase() ' one arg only • Trim(), Rtrim() and Ltrim() ' one arg only • Val(strA) ' change a string to a number • Cstr(intX) ' change a number to a string • Because Cstr(57) returns " 57" not "57" use Trim(Cstr(intX))

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