Repetition Chapter 6 - Visual Basic Schneider 1

 Loop Structure  Elements of a Loop Structure  Processing Lists of Data with Do Loops Chapter 6 - Visual Basic Schneider2

 Do While ……. Loop  Do Until …… Loop  For …… Next loop Chapter 6 - Visual Basic Schneider3

 Looping: the process of repeating a series of statements multiple times until a criteria is met Chapter 6 - Visual Basic Schneider4

 Loop control variable: A variable used to determine whether a loop will be executed  Loop body: The statement (s) that are executed each time a loop repeats Chapter 6 - Visual Basic Schneider5

Do While condition is true statement(s) Loop Chapter 6 - Visual Basic Schneider6

7 Is the condition true Execute statements within the loop Execute statements that follow the loop Yes No

Private Sub cmdDisplay_Click() Dim num As Integer ' Display the numbers from 1 to 10 num = 1 Do While num <= 10 picNumbers.Print num; num = num + 1 Loop End Sub Chapter 6 - Visual Basic Schneider8

 Is executed as long as the condition is True.  If condition is False then the next statement after the Loop is executed. Chapter 6 - Visual Basic Schneider9

 Methods of controlling loops: ◦ Counter-controlled loops  repeat a specific number of times ◦ Event-controlled loops  repeat until something happens in the loop body to change the value of loop control variable. Chapter 6 - Visual Basic Schneider10

passWord = "" Do While passWord <> "SHAZAM" passWord = UCase(InputBox("What is the password?")) Loop Chapter 6 - Visual Basic Schneider11

 Is useful when the programmer knows how many times the loop should be executed.  Initialize the counter by setting it to a beginning value before entering the loop.  The counter is incremented (or decremented) by the same value during each repetition. Chapter 6 - Visual Basic Schneider12

num = 1 Do While num <= 10 picOutput.Print num; num = num + 1 Loop Chapter 6 - Visual Basic Schneider13

 Is executed until the condition becomes True  Any Do While…. Loop can be rewritten as a Do Until ….. Loop Chapter 6 - Visual Basic Schneider14

Private Sub cmdDisplay_Click() Dim passWord As String, info As String If UCase(txtName.Text) = "SECRET.TXT" Then Do passWord = UCase(InputBox("What is the password?")) Loop Until passWord = "SHAZAM" End If Open txtName.Text For Input As #1 Input #1, info picItem.Cls picItem.Print info Close #1 End Sub Chapter 6 - Visual Basic Schneider15

Private Sub cmdEstimate_Click() Dim amt As Single, yrs As Integer ' Years to deplete savings account picResult.Cls amt = yrs = 0 Do amt = amt * yrs = yrs + 1 Loop Until amt <= 0 picResult.Print "It takes"; yrs; "years to deplete the account." End Sub Chapter 6 - Visual Basic Schneider16

 The Do While … Loop executes while the condition is true  The Do Until….. Loop executes until the condition is true  Both can be used to create any type of loop Chapter 6 - Visual Basic Schneider17

 EOF(n) is True if the end of the file having reference number n has been reached. Otherwise, it is False  Example: Open “PHONE.TXT” for Input As #1 Do While Not EOF(1) Input #1, nom, phoneNum picOutput.Print nom, phoneNum Loop Close #1 Chapter 6 - Visual Basic Schneider18

 A counter is a numeric variable that keeps track of the number of items that have been processed in a loop.  An accumulator is a numeric variable that holds a sub-total during multiple passes through a loop. Chapter 6 - Visual Basic Schneider19

Private Sub cmdAnalyze_Click() Dim numCoins As Integer, sum As Single, value As Single Open "COINS.TXT" For Input As #1 numCoins = 0 sum = 0 Do While Not EOF(1) Input #1, value numCoins = numCoins + 1 sum = sum + value Loop picValue.Print "The value of the"; numCoins; "coins is"; sum; "cents." End Sub Chapter 6 - Visual Basic Schneider20

 Do While ……. Loop  Do ……. Loop While  Do ……. Loop Until  Do Until ……. Loop Chapter 6 - Visual Basic Schneider21

num = 11 Do While num <= 10 picOutput.Print num; num = num + 1 Loop Chapter 6 - Visual Basic Schneider22 num = 11 Do picOutput.Print num; num = num + 1 Loop until num <= 10 How many times will the following loops execute?

Do While i < 10 i = i + 1 Loop Chapter 6 - Visual Basic Schneider23 Do i = i + 1 Loop While i < 10 Which loop is infinite? Do Until i < 10 Loop Do i = i + 10 Loop Until i < 10

 A loop where the number of iterations is determined by a range of values for a numeric variable  Syntax: For controlVariable = initial To terminal statement(s) Next controlVariable Chapter 6 - Visual Basic Schneider24

Private Sub cmdDisplayTable_Click() Dim i As Integer ‘Display a table of the first 5 numbers and their squares For i = 1 To 5 picTable.Print i; i ^ 2 Next i End Sub Chapter 6 - Visual Basic Schneider25 Initial Value Control variable Terminating value

Dim numVar As Integer For numVar = 1 To 5 Step 2 picOutput.Print numVar; Next numVar Output: Chapter 6 - Visual Basic Schneider26

1. The control variable is assigned the initial value. 2. After each loop iteration, the step value is added to the value of the control variable. (If there is no step value, 1 is added.) 3. Iteration continues until the terminating value is exceeded. Chapter 6 - Visual Basic Schneider27

 You should never modify the value of the loop control variable in the loop body.  Each For loop must end with a Next statement. Chapter 6 - Visual Basic Schneider28

Private Sub cmdDisplay_Click() Dim i As Integer For i = 1 To 10 picOutput.Print "*"; Next i End Sub Output: ********** Chapter 6 - Visual Basic Schneider29

Private Sub cmdDisplay_Click() Dim i As Integer, stars As Integer stars = Val(InputBox("Row length (1-20) : ")) For i = 1 To stars picOutput.Print "*"; Next i End Sub Chapter 6 - Visual Basic Schneider30

Dim numVar As Integer For numVar = 8 To 1 Step -2 picOutput.Print numVar; Next numVar Output: Chapter 6 - Visual Basic Schneider31

For outer = 1 To 4 For inner = 1 To 2.. Next inner Next outer Chapter 6 - Visual Basic Schneider32

Private Sub cmdDisplay_Click() Dim i As Integer, j As Integer For i = 1 To 10 For j = 1 To 10 picOutput.Print "*"; Next j picOutput.Print Next i End Sub Chapter 6 - Visual Basic Schneider33

For i= -5 To -1 Step - 2 picOutput.Print i; Next i picOutput.Print i; Chapter 6 - Visual Basic Schneider34 For i= 1 To 5 Step 2 i=i+1 picOutput.Print i; Next i picOutput.Print i;

Private Sub cmdDisplay_Click() Dim i As Integer, j As Integer For i = 1 To 10 For j = i To 10 picOutput.Print "*"; Next j picOutput.Print Next i End Sub Chapter 6 - Visual Basic Schneider35 Private Sub cmdDisplay_Click() Dim i As Integer, j As Integer For i = 1 To 10 For j = 1 To i picOutput.Print "*"; Next j picOutput.Print Next i End Sub