UTPA – Fall 2011

1. CSCI 3327 Visual Basic Chapter 4: Control Statements in Visual Basic (Part 2) UTPA – Fall 2011

2. Objectives • In this chapter, you will: • Learn more control structures • Repetition statements • For … Next, Do … Loop While, Do … Loop Until • Selection • Select … Case • Know how to use Exit and Continue statements to break or terminate the current iteration • Learn how to use logical operators

3. In the Last Class: Repetition Structure • Visual Basic provides 7 repetition statements • Do While … Loop • While … End While • Do Until … Loop • Do … Loop While • Do … Loop Until • For … Next • For Each … Next

4. Example of For … Next Repetition Statement • Output even numbers between 2 and 10 • For counter AsInteger = 2 To 10 Step 2 • outputLabel.Text &= counter & " " • Next

5. Discussions on For … Next Repetition Statement • For counter AsInteger = 2 To 10 Step 2 … Next • Keywords: For, To, Step, Next • "counter AsInteger" declares a counter of integer data type • counter – control variable name • Integer – control variable type • Initial value of control variable – 2 • Final value of control variable – 10

6. Discussions on For … Next Repetition Statement (cont'd) • For counter AsInteger = 2 To 10 Step 2 … Next • Increment of control variable – Step 2 • If "Step 2" is missing, the default value is 1 • Output all integers from 2 to 10 • For counter AsInteger = 2 To 10 outputLabel.Text &= counter & " " Next • Result: 2, 3, 4, 5, 6, 7, 8, 9, 10

7. General Form of a For … Next Statement • ForinitializationTofinalValueStepincrement statement Next

8. Other Examples of For … Next (1) • Declaring the control variable before a For…Next Statement • Dim counter AsInteger For counter = 2 To 10 Step 2 outputLabel.Text &=counter & " " Next • Using expressions in the For…Next statement • For j AsInteger = x To 4*x*y Step y \ x

9. Other Examples of For … Next (2) • Default increment: 1 • For i = 1 To 100 • For i = 1 To 100 Step 1 • Decrement • For i = 100To1Step-1

10. Example 5.5: InterestCalculator.vb • URL: http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html

11. Example 5.5: InterestCalculator.vb (cont'd) • NumericUpDown control • Minimum property • Maximum property • Increment property • Value property

12. Example 5.5: InterestCalculator.vb (cont'd) • Val(…) function • Convert strings to numbers • Dim principal AsDecimal = Val(principalTextBox.Text) • Ignores white space in the string • E.g. "33 5" will be converted to 335 • vbTab • Format by adding a tab

13. Example 5.5: InterestCalculator.vb (cont'd) • String.Format("{0:C}", amount) • Output variable amount in currency format • E.g., $1,050.00 • TextChanged event of controls TextBox and NumericUpDown • resultListBox.Items.Clear()

14. Nested Repetition Statements • For i = 1 To 10 Step 1 For j = 1 To 20 Step 2 … Next i Next j

15. Example 5.8: SquareOfCharacters.vb • URL: http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html

16. Example 5.8: SquareOfCharacters.vb (cont'd) • For row AsInteger = 1 To sideLength • For column AsInteger = 1 To sideLength • outputTextBox.AppendText(fillCharacter & " ") • Next column • outputTextBox.AppendText(vbCrLf) • Next row

17. Do…Loop While and Do…Loop Until Repetition Statements • The loop body is always executed at least once Dim product AsInteger = 1 Do product = product * 3 Loop While product <=100 ------------------------------------------------------------------------------- Dim product AsInteger = 1 Do product = product * 3 Loop Until product >100

18. Use Exit to Terminate Repetition Statements • Exit Do • Terminate the repetition statements such as: • Do While…Loop, Do Until…Loop, Do…Loop While, Do…Loop Until • Exit For • Terminate For…Next • Exit While • Terminate While…End While • Exit Select • Terminate Select…Case

19. Use Continue in Repetition Statements • Continue statementonly terminates the current iteration • Continue Do • Terminate the repetition statements such as: • Do While…Loop, Do Until…Loop, Do…Loop While, Do…Loop Until • Continue For • Terminate For…Next • Continue While • Terminate While…End While

20. In the Last Class: Selection Structure • If … Then • If … Then … Else • Select … Case [grade>=60] display "passed" [grade<60]

21. Multiple-Selection Statement:Select … Case SelectCase grade Case 100 perfectScoreCount += 1 ' increment perfectScoreCount aCount += 1 ' increment aCount Case 90 To 99 ' grade was between 90 and 99 aCount += 1 ' increment aCount Case 80 To 89 ' grade was between 80 and 89 bCount += 1 ' increment bCount Case 70 To 79 ' grade was between 70 and 79 cCount += 1 ' increment cCount Case 60 To 69 ' grade was between 60 and 69 dCount += 1 ' increment dCount CaseElse ' grade was less than 60 fCount += 1 ' increment fCount EndSelect

22. Multiple-Selection Statement:Select … Case • Case Else is optional • If no case matches and there is no Case Else, then program control continues with the first statement after Select … Case • End Select terminates the Select … Case statement

23. Example 5.9: ClassAverage.vb • URL: http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html • TextBox • gradeTextBox.Focus() gives the focus to the gradeTextBox • String.Empty

24. Logical Operators • Logical And operator • If gender = "F" And age >=65 Then • seniorFemales += 1 • End If

25. Logical Operators (cont'd) • Logical Or Operator

26. Short-Circuit Evaluation • AndAlso • If gender = "F" AndAlso age >=65 • If gender is not "F", then "age >=65" will not be evaluated • OrElse • If gender = "F" OrElse age >=65 • If gender is "F", then "age >=65" will not be evalutated

27. Other Logical Operators • Logical Xor operator • Logical Not operator • IfNot (value = 0) Then …

28. Rules of Operator Precedence priority • ^ • +, - (sign operations) • *, / • \ • Mod • +, - (addition and subtraction) • & • =, <>, <, <=, >, >= (equality and relational) • Not • And, AndAlso • Or, OrElse • Xor • =, +=, -=, *=, /=, \=, ^=, &= high low