Types of LOOP Structures Do While ……. Loop Do Until …… Loop For …… Next loop

Basic Definition Looping: the process of repeating a series of statements multiple times until a criteria is met

Basic Components of Loops 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

The Do While ……. Loop Do While condition is true statement(s) Loop

Flowchart for a Do While Loop Is the condition true Execute statements within the loop Execute statements that follow the loop Yes No

Example What is the output?

Output (Displays the numbers from 1 through 10)

The Do While ……. Loop Is executed as long as the condition is True. If condition is False then the next statement after the Loop is executed.

Controlling Loops 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.

Example of event-controlled loops strPassWord = "" Do While strPassWord <> “BIS" strPassWord = UCase(InputBox("What is the password?")) Loop

Counter-controlled Loops 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.

Example intNum = 1 Do While intNum <= 10 picOutput.Print num; intNum = intNum + 1 Loop

Do Until ……. Loop Is executed until the condition becomes True Any Do While…. Loop can be rewritten as a Do Until ….. Loop

$15000 is deposited at 5% interest. If $1000 years to deplete a saving account) is withdrawn at the end of each year, how many years will it take to empty the account?

Comparing While… and Until Loops 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

EOF Function 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

Counters and Accumulators 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.

Example: Counter & Accumulator 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

For … Next Loop 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

Example 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 Initial Value Control variable Terminating value

Example Dim numVar As Integer For numVar = 1 To 5 Step 2 picOutput.Print numVar; Next numVar Output: 1 3 5

When a For statement is encountered The control variable is assigned the initial value. 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.) Iteration continues until the terminating value is exceeded.

Rules for Using For... Next loop You should never modify the value of the loop control variable in the loop body. Each For loop must end with a Next statement.

Example Private Sub cmdDisplay_Click() Dim i As Integer For i = 1 To 10 picOutput.Print "*"; Next i End Sub Output: **********

Example 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

Example Dim numVar As Integer For numVar = 8 To 1 Step -2 picOutput.Print numVar; Next numVar Output:

Nested Loops For outer = 1 To 4 For inner = 1 To 2.. Next inner Next outer

Example: Display a 10x10 rectangle of stars 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