RND
Returns a random double precision number in the range [0, 1)
Syntax:
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 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:
- For fbc version < 1.08, Rnd is not thread-safe. Used in the context of a multi-threaded program with race conditions due to asynchronous calls to Rnd, many values are temporarily returned in duplicate for a same thread.
- For fbc version >= 1.08, Rnd is became 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. Structures for other random number generators are also now available in the standard header "fbmath.bi".
- For fbc version >= 1.08, Rnd is became 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. Structures for other random number generators are also now available in the standard header "fbmath.bi".
Examples:
'' 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))
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))
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:
Back to Math
