"Dim x()" - Dynamic-Size Array Example

VBScript Tutorials - Herong's Tutorial Examples

∟"Dim x()" - Dynamic-Size Array Example

This section provides a tutorial example on how to declare a dynamic-size array 'Dim x()'. 'ReDim x(n)' statement must be used on to set the size of a dynamic-size array before it can be used.

We learned from previous sections that a dynamic-size array must be declared with a no size. For example, "Dim x()" declares a dynamic-size array, x, with no upper bound limit. You must set the size of x with a statement like "ReDim x(99)" before you can use it.

One important nature of a dynamic-size array is that it can be re-sized with a "ReDim Preserve x(n)" statement. The keyword "Preserve" is important, if you want to keep all old values in the array.

To show you how a dynamic-size array works, I wrote the following example, array_dynamic_size.html:

<html>
<body>
<!-- array_dynamic_size.html
 - Copyright (c) 1998 HerongYang.com. All Rights Reserved.
-->
<pre>
<script language="vbscript">
   document.writeln("")
   Dim aYear()
   document.writeln("Check 1: Is aYear an array? " & IsArray(aYear))

'   aYear(0) = "Jan"   'Error 1: Subscription out of range

'   iSize = UBound(aYear)+1 'Error 2: Index out of range

   ReDim aYear(5)
   document.writeln("Check 2: Is aYear an array? " & IsArray(aYear))

   aYear(0) = "Jan"
   aYear(1) = "Feb"
   aYear(5) = "Jun"
   
   ReDim Preserve aYear(11)
   aYear(10) = "Nov"
   document.writeln("Months in a year:")
   For i=LBound(aYear) To UBound(aYear)
      document.writeln("   " & i & " = " & aYear(i))
   Next
</script>
</pre>
</body>
</html>

Here is the output:

Check 1: Is aYear an array? True
Check 2: Is aYear an array? True
Months in a year:
   0 = Jan
   1 = Feb
   2 = 
   3 = 
   4 = 
   5 = Jun
   6 = 
   7 = 
   8 = 
   9 = 
   10 = Nov
   11 =

Note that:

Output message "Check 1" shows that a dynamic-size array is an array event if its size is not set yet.
Commented out "Error 2" shows that "UBound" can not be used is array's size is not set yet.