each item can either be accessed in a sequential order, or
through supplying its index position.
Consider this:
<script language="VBScript">
dim names(5)
names(0)="Rohit" names(1)="Prakash" names(2)="Asha"
names(3)="Tom" names(4)="Lata" names(5)="Kailash"
for i=0 to 5 document.write names(i) & "
" next
</script>
Here we declare an index of dimension 5, which later on, comes
to store six names, as, an index in an array starts at 0.
Then the for loops dumps the entire array onto the HTML page.
People familiar with the for() {.} loop of JavaScript will
notice that the for.next loop of VBScript is less cryptic.
Since now we have learnt how to create a VBScript array, let us
try to sort this array. We'll sort the array in ascending order,
that is, from the lowest to the top most in the alphabetical
array.
So what's the logic?
1. Compare the first name with the second name 2. If the second
name is lower than the first name, then swap 3. else 4. Compare
the first name with the third name 5. If the third name is lower
than the first name, then swap 6. else 7. Compare the first name
with the fourth name 8. If the fourth name is lower than the
first name, then swap 9. else 10. Compare the first name with
the fifth name 11. If the fifth name is lower than the first
name, then swap
So by the time we have reached the 11th step, we have the lowest
name at the first position.
The second round starts at the second index index, as the first
we already know is the lowest.
1. Compare the second name with the third name 2. If the third
name is lower than the second name, then swap 3. else 4. Compare
the second name with the fourth name
and so on
I hope you've understood the logic now. Let's see how it looks
programmatically:
<script language="VBScript">
dim names(5) names(0)="Rohit" names(1)="Prakash" names(2)="Asha"
names(3)="Tom" names(4)="Lata" names(5)="Kailash"
for i=0 to 4 for j=i+1 to 5 if names(i)>names(j) then
temp=names(j) names(j)=names(i) names(i)=temp end if next next
for i=0 to 5 document.write names(i) & "
" next
</script>
There is a nested loop here. Study the flow of the for i=0 to 4
loop. The outer loop holds the index of the item that will be
compared with every other, next item. For instance, when the
first cycle of the loop begins, i is zero, and when the program
ends the nested loop, j starts at i+1, that is, 1. So turn by
turn, item at index zero is compared with every item in the
array. The outer array goes only till 4 because when the nested
loop begins, the second last item will be compared with the last
item: j=i+1
Save the file, and check it out in your browser.
Now we see the use of a dynamically defined array, and how that
array can be filled using the inputbox() function.
<script language="VBScript">
dim strings() i=0 redim strings(i)
strings(i)=""
do
holdstring=inputbox("Please enter a string, 'fin' to stop.")
if holdstring<>"fin" then
strings(i)=holdstring i=i+1 redim preserve strings(i)
else
exit do
end if
loop
if strings(0)<>"" then
for j=0 to i
document.write strings(j) & "
"
next
end if
</script>
strings is an array that is re-dimensioned whenever the user
types in a new string. When we declare an array, we reserve the
memory space for that array, that is, if we say
dim arr(20)
it means we are reserving the space for twenty data items. But
what if the user enters just five items? The rest of the space
is wasted. To avoid this, we declare a dynamic array.
In the above script, we have a loop whose continuance depends on
the user input. It keeps on loop until the user enters "fin".
So, when "fin" is not entered, only then the dimension of the
array strings is increased.
When we are re-dimensioning an array, we have to use the keyword
preserve to preserve the existing content of the array. In its
absence, the array gets re-dimensioned, but the values are lost.
Exit do forces the program to come out of the loop if the
condition that terminates it, occurs.
Amrit Hallan is a freelance web designer.
