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VBScript General and Maths.

General Introduction

VBScript itself needs to be used with an environment providing resources, mostly I/O, to work with. Environments include Web pages, Windows Scripting Host, and programs such as Excel and Word.

 DosBoxPrompt> CScript //?
 DosBoxPrompt> WScript //?

 Command Line : Wscript.Echo '' not Cscript.Echo ?
 Web Script   : document.write

 Continuation : underline _

 Option Explicit '' To require declarations

It appears that PowerShell is intended to take the place of VBScript - Install UK. News:microsoft.public.windows.powershell exists.

These Pages

These VBScript pages are largely about VBScript as used in Web pages; but, in WSH, CScript and WScript are rather similar. I do not know much about these languages yet - there is a little in my MS-DOS Batch Files.

The examples given here all work, obviously, in a Web page (or, at least, they do so locally on my system); some of the algorithms have been tested at the command line. Use View Source. Test carefully before serious use.

 '' : Comment quote is doubled here, to avoid confusing Tidy

See also JavaScript Index & Introduction and Pascal Introduction, for code that could be translated to VBScript.

Event Handlers

VBScript is invoked as the first scripting on this page → ←.

Therefore, even though some later code on the page could be JavaScript, VBScript will be used for all event handlers. For convenience, Option Explicit is preset in that script.

MH wrote  : You can disambiguate by using

    onsomeeventname='javascript:foo();'
    onsomeeventname='vbscript:call foo()'
    onsomeeventname='vbscript:foo'

Code Display

I have found no means in VBScript of displaying the code of a function given only its name; therefore, I have no equivalent of the colour-bordered boxes that I use in JavaScript. Here, copies of blocks of code to be executed, and their output, will be colour-coded as follows :-

document.write "The result of the code" '' is below

Other output is

To be certain about just what code is executed, view the source code of the page.

Code fragments - VBScript, JavaScript, HTML - can be tested as in JavaScript/HTML/VBS Quick Trials

D = Now '' A sample code fragment

You are using  

Padding

function Widen(X, L) '' X, to width L
  Widen = Space(L-Len(X)) & X
end function

Regular Expressions

Regular Expressions became available, I believe, at VBS Version 5.

In recent systems, VBScript (in Web pages) and VBS (for execution at a Windows MS-DOS Prompt by CSCRIPT or in the GUI by WSCRIPT) have RegExps.

I acquired IE6 (from 2006-10-19) and now use IE8, but have scarcely started using VBScript RegExps.

• Regular Expressions
• Win32 - Windows Scripting Host, VBScript in WSH, RegExp Example
• VBScript Regular Expressions

Maths

Numbers

Floating-point numbers have the usual potential for rounding errors, as in JavaScript Maths.

In your browser,

X = 1/7 : document.write 1.0-(X+X+X+X+X+X+X)

writes  

I get 2.22044604925031E-16 = 2^-52.

The actual value is evidently held in binary as an IEEE Standard 754 number of type Double. See Pascal Floating-Point for links to general information on floating-point numbers and arithmetic, and Pascal / Delphi / + Types for data on IEEE number representation, and JavaScript Maths.

Format

  FormatNumber(X, n)
  FormatCurrency(X, n) '' Uses Windows currency sign

Those convert X to a string with n decimal places.

Decimal Separator

I suspect that both "." and "," are possible, depending on location setting.

Random Numbers

Randomize alone loads the generator seed from the Timer function; it should, almost always, be used only once per program, such as at the beginning. Note that Timer has a resolution of 0.01 s, and may be updated at only 18.2 Hz. The generator is only 24-bit.

Randomize N uses N to load the seed (range of N ?), and can be used as required.

Function Rnd should give results in the range 0 to 1. Try something like :-

Randomize 5
for K = 1 to 15
  R = Rnd
  document.writeln R, "  	", R*16777216 '' 2^24
  next

Internals

The generator is said to use   X_n+1 = ( X_n × 16598013 + 12820163 ) mod 16777216   and the result of function Rnd is that divided by 16777216. That will be confirmed if the integer part of the following output (calculated in JavaScript by that expression in your browser) matches the previous.

Random()

Presuming that 0 ≤ Rnd < 1.0 :-

function Random(N) '' Return a random integer in 0..(N-1)
  Random = Int(N*Rnd)
  end function

Dim K
Randomize
for K = 1 to 50
  document.write Random(5)
  next

Gives for N = 5 :-

Shuffle

This is the efficient Fisher-Yates / Durstenfeld / Knuth shuffle. Use menu View Source to see the code. The core of it is :-

For K = 1 to L : J = L-K
  X = Random(J+1) : T = A(J) : A(J) = A(X) : A(X) = T '' Swap A(X) A(J)

For More

See also JavaScript Random and Borland Pascal/Delphi Random, for code that could be translated to VBScript, including for shuffle, deal, and draw.

Donald E Knuth :- "Random numbers should not be generated with a method chosen at random".

ArcTan2

ArcTan2(Y, X) gives the angle measured anti-clockwise from the line Y=0 to the point X, Y in radians.

This tests one of two (see source) functions for ArcTan2(Y, X) which appears not natively available (an untested Pascal version is in Pascal Maths) :-

One can determine ArcTan2(Y, X) as 2*Atn(Fn(Y, X)) for some Fn(Y, X) which seems elegant. The results of the two functions differ only by O(LSB).

Combinations and Permutations

Obviously the string S can be split and used to index an array of things-to-be-combined-or-permuted. One may prefer to replace the write by something that adds S as a new element of an array, or to replace S & J similarly.

The implementations are not necessarily optimum.

Combinations

Each element is either present or absent; elements occur in order. Note where the first output line represents the empty set.

function Comb(M, N, S)
  dim J
  document.writeln S, "."
  for J = M to N : call Comb(J+1, N, S & J) : next
  end function

call Comb(0, 3, "Comb ")

The algorithm is to select an element from those as yet unchosen, and then either to stop or to select from those higher ones remaining.

Permutations

All elements are present; all orders occur.

function Perm(A, M, N, S)
  dim J
  if M<0 then document.writeln S, "."
  for J = 0 to N
    if A(J) then A(J) = False : call Perm(A, M-1, N, S & J) : A(J) = True
    next
  end function

dim A(9), K
for K = 0 to 9 : A(K) = True : next

call Perm(A, 2, 2, "Perm ")

The algorithm is to recursively select an element from those as yet unchosen. Another approach would be to take all possible orders of each combination. Remove M to get all ordered selections.

Speed

While script size and speed may often not be of much importance, it is good to use the best method, and instructive to investigate what that might be in various cases.

Extend

It is often necessary to convert a Number to a fixed-length string with leading zeroes. This compares

  St = Right(10000+K,4) ' Add
  St = Right("000"&K,4) ' Cat

In IE4, I found Add to be on average a little faster than Cat; and similarly in WSH cscript. ?????

YYYYMMDD

It is often necessary to convert a CDate to a string YYYYMMDD. This compares

  St = CStr(Y*10000+M*100+D) ' Add
  St = Y & Right("0"&M, 2) & Right("0"&D, 2) ' Cat

In IE4, I found Add to be on average about 2.7 times faster than Cat; and similarly in WSH cscript.

Interestingly, using 1e4,1e2 instead of 10000,100 is much slower

hhmmss

It is often necessary to convert a CDate to a string hhmmss. This compares

  St = Right(1000000+h*10000+m*100+s, 6) ' Add
  St = Right("0"&h, 2) & Right("0"&m, 2) & Right("0"&s, 2) ' Cat

??? In IE4, I found Add to be on average about 3.1 times faster than Cat; and similarly in WSH cscript.

Sorting

A QuickSort.

Test Box

This is cut down from JavaScript/HTML/VBS Quick Trials. Give VBScript in the textarea, using document.write or other means of observing its effect.