Randomize
 
Seeds the random number generator

Syntax

Declare Sub Randomize ( ByVal seed As Double = -1.0, ByVal algorithm As Integer = 0 )

Usage

Randomize [ seed ][, algorithm ]

Parameters

seed
A Double seed value for the random number generator. If omitted or set to -1.0, the Timer value will be used instead.
algorithm
An Integer value to select the algorithm used. If omitted, the default algorithm for the current language dialect is used.

Description

Sets the random seed that helps Rnd generate random numbers, and selects the algorithm to use. Valid values for algorithm are:

0 - Default for current language dialect. This is algorithm 3 in the -lang fb dialect, 4 in the -lang qb dialect and 1 in the -lang fblite dialect.
1 - Uses the C runtime library's rand() function. This will give different results depending on the platform.
2 - Uses a fast implementation. This should be stable across all platforms, and provides 32-bit granularity, reasonable degree of randomness.
3 - Uses the Mersenne Twister. This should be stable across all platforms, provides 32-bit granularity, and gives a high degree of randomness.
4 - Uses a QB compatible function. This should be stable across all platforms, and provides 24-bit precision, with a low degree of randomness.

For good results, using a seed that is not quite predictable should be used - for example, the value returned from Timer. This should not be done too frequently though, because for the non-QB algorithms the integer value is used, so the seed will only change once a second, and calling Randomize with the same seed will reset the sequence.

When you call Randomize in QB compatible mode, part of the old seed is retained. This means that if you call Randomize several times with the same seed, you will not get the same sequence each time. To get a specific sequence in QB compatible mode, set the seed by calling Rnd with a negative parameter.

Example

'' Seed the RNG, which is set to C's rand().
Randomize Timer, 1


Differences from QB

  • Second parameter new to FreeBASIC.

See also