CSCI 3327 Visual Basic Chapter 4: Control Statements in Visual Basic (Part 2) UTPA – Fall 2011 Part of the slides is from Dr. John Abraham’s previous lecture slides. – Xiang Lian

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

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

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

Discussions on For … Next Repetition Statement For counter As Integer = 2 To 10 Step 2 … Next Keywords: For, To, Step, Next "counter As Integer" 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

Discussions on For … Next Repetition Statement (cont'd) For counter As Integer = 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 As Integer = 2 To 10 outputLabel.Text &= counter & " " Next Result: 2, 3, 4, 5, 6, 7, 8, 9, 10

General Form of a For … Next Statement For initialization To finalValue Step increment statement Next

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

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

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

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

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

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()

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

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

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

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

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

Use Continue in Repetition Statements Continue statement only 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

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

Multiple-Selection Statement: Select … Case Select Case grade Case 100 perfectScoreCount += 1 ' increment perfectScoreCount aCount += 1 ' increment aCount Case 90 To 99 ' grade was between 90 and 99 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 Case Else ' grade was less than 60 fCount += 1 ' increment fCount End Select

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

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

Expression 1 And Expression 2 Logical Operators Logical And operator If gender = "F" And age >=65 Then seniorFemales += 1 End If Expression 1 Expression 2 Expression 1 And Expression 2 False True

Logical Operators (cont'd) Logical Or Operator Expression 1 Expression 2 Expression 1 Or Expression 2 False True

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

Other Logical Operators Logical Xor operator Logical Not operator If Not (value = 0) Then … Expression 1 Expression 2 Expression 1 Xor Expression 2 False True

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