VB2010 Lesson 11- Looping
|
Visual Basic 2010 allows a procedure to be repeated as many times as long as the processor and memory could support. This is generally called looping . Looping is required when we need to process something repetitively until a certain condition is met. For example, we can design a program that adds a series of numbers until the sum exceeds a certain value, or a program that asks the user to enter data repeatedly until he/she keys in the word 'Finish'. In Visual Basic 2010, we have three types of Loops, they are the For.....Next loop, the Do loop. and the While.....End while loop
For counter=startNumber to
endNumber (Step increment) One or
more VB statements Next Sometimes the user
might want to get out from the loop before the whole
repetitive
process is executed, the command to use is Exit For. To
exit a For.....Next Loop, you can place the Exit For statement
within the loop; and it is normally used together with the
If....Then.....sstatement. For its application, you can refer
to example 11.1 d.
Example 11.1 a
Dim counter as Integer For counter=1 to 10
ListBox1.Items.Add
(counter) Next
* The program
will enter number 1 to 10 into the list box. Example
11.1b Dim counter , sum As
Integer For counter=1 to
100 step 10 sum+=counter ListBox1.Items.Add
(sum) Next
* The program will
calculate the sum of the numbers as
follows:
sum=0+10+20+30+40+...... Example
11.1c Dim counter, sum As
Integer *Notice that increment
can be negative.
The program will compute
the
subtraction as
follow:
1000-100-95-90-..........
Example
11.1d Dim n as
Integer For n=1 to 10 If n>6
then Exit For End If Else ListBox1.Items.Add ( n) Next
End If Next The process will stop
when n is greater than 6. 11.2 Do
Loop The formats are a) Do While condition
Block of one or more VB statements Loop
b)
Do Block
of one or more VB statements c) Do Until
condition d)
Do
Block of one or more VB statements
Loop Until condition *
Exiting the Loop Sometime we need exit to exit a
loop prematurely because of a certain condition is fulfilled. The syntax
to use is known as Exit Do. Lets examine the following
examples Example
11.2(a)
Do while counter <=1000
TextBox1.Text=counter
counter +=1
Loop * The above example will keep on
adding until counter >1000. The above example can be rewritten
as
Do
TextBox1.Text=counter
Loop until counter>1000 Example
11.2(b) Private Sub Button1_Click(ByVal
sender As System.Object, ByVal e As System.EventArgs) Handles
Button1.Click ListBox1.Items.Add( ListBox1.Items.Add( If
n = 100 Then End
Sub In the
above example, we find the arithmatic summation of
1+2+3+4+......+100. In the
design stage,
you need to insert a ListBox into the form for displaying the
output The
program uses the Add method to populate the ListBox.
The statement ListBox1.Items.Add("n" & vbTab
& "sum") will display the headings in the ListBox,
where
it uses the vbTab function to
create a space between the heading n and sum.
The
statement ListBox1.Items.Add(n & vbTab & sum)
will list the number n and the values of the arithmatic
summation The
output is displayed below: 11.3 While
...End While Loop The structure of a While....End
While is very similar to the Do Loop. it takes
the following
format: While
condition
Statements End While The above loop means that while the
condition is not met, the loop will go on. The loop will end when the
condition is met. Example
11.3 Dim sum, n As
Integer Private Sub Button1_Click(ByVal
sender As System.Object, ByVal e As System.EventArgs) Handles
Button1.Click
Copyright 2010 Dr.Liew Voon Kiong . All rights reserved |Contact: admin@vbtutor.net [Privacy Policy] |
