Rnd
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".
Example
`
'' 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))
`
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:

`Rnd` was not thread-safe (many values temporarily returned in duplicate for a same thread).
The standard "fbmath.bi" header for available algorithms did not exist.
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`