RND

• Source: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgRnd
• Last revised: 2022-04-14

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Returns a random double precision number in the range [0, 1)

Syntax

` declare function Rnd ( byval seed as single = 1.0 ) as double

`

Usage

` result = Rnd( seed )

`

Parameters

seed

Optional single argument. If seed has a value of zero (0.0), the last random number generated is repeate. For any other number a new random number is returned. With the QB-compatible algorithm, a negative number fully reseeds the generator. The default for no argument is to return a new random number.

Return Value

Returns the random number generated.

Description

Returns a number of type double in the range [0, 1) (i.e. 0 <= Rnd < 1), based on a random seed (see Randomize).

Rnd can use a variety of different algorithms - see Randomize for details of the default and selectable algorithms.

Rnd will return the same sequence of numbers every time a program is run. This sequence can be changed by reseeding the generator.

Note:

Rnd is thread-safe (by using an internal mutex), but not thread specific. Used in the context of a multi-threaded program, only the execution speed is significantly slowed down compared to a single thread call context.

Unfinished structures for other random number generators are also available in the standard header "fbprng.bi".

Examples

start GeSHi

'' Function to a random number in the range [first, last), or {first <= x < last}.
Function rnd_range (first As Double, last As Double) As Double
    Function = Rnd * (last - first) + first
End Function

'' seed the random number generator, so the sequence is not the same each time
Randomize

'' prints a random number in the range [0, 1), or {0 <= x < 1}.
Print Rnd

'' prints a random number in the range [0, 10), or  {0 <= x < 10}.
Print Rnd * 10

'' prints a random integral number in the range  [1, 10], or {1 <= n <= 10}.
''     (because: 0 <= Rnd * 10 < 10)
Print Int(Rnd * 10) + 1

'' prints a random integral number in the range [69, 420], or {69 <= n <= 420}.
''     (because: 69 <= rnd_range(69, 421) < 421)
Print Int(rnd_range(69, 421))

end GeSHi

Version

• Before fbc 1.10.0 (for fbc 1.08.0 and fbc 1.09.0), "fbprng.bi" was named "fbmath.bi".
• Before fbc 1.08.0:

Dialect Differences

The default algorithm used depends on the current dialect in use:

• With the -lang fb dialect, a 32 bit Mersenne Twister function with a granularity of 32 bits is used.
• With the -lang qb dialect, a function giving the same output as Rnd in QB is used. The granularity is 24 bits.
• With the -lang deprecated and -lang fblite dialects, the function in the C runtime available in the system is used. The function available in Win32 has a granularity of 15 bits, and 32 bits in Linux and DOS.

Differences from QB

• None, if compiled in the -lang qb dialect. Other dialects can also use the same seeding and generating algorithms by calling Randomize with the appropriate parameter.
• For the non-QB-compatible algorithms, if the optional argument is less than 0, it has the same meaning as passing an argument of 1.

See also

• Randomize
• Timer
• Int

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