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110 lines
4.3 KiB
Plaintext
110 lines
4.3 KiB
Plaintext
The '''RND''' function returns a random number with a value between 0 (inclusive) and 1 (exclusive).
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{{PageSyntax}}
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:: result! = [[RND]] [(''n'')]
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{{Parameters}}
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* ''n'' is a [[SINGLE]] numeric value that defines the behavior of the RND function but is '''NOT normally required''':
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::n parameter omitted: Returns next random number in the sequence.
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::n = 0: Return the last value returned.
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::n < 0: Always returns the same value for any given n
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::n > 0: the sequence of numbers generated will not change unless [[RANDOMIZE]] is initiated.
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{{PageDescription}}
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* The random numbers generated range from 0 minimum to .9999999 maximum [[SINGLE]] values that never equal 1.
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* To get values in a range larger than 1, multiply RND with a number to get returns up to but not including that numerical value.
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* To get values starting at a certain number, add that number to the RND result as RND minimums can be 0.
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* If you need an integer range of numbers, like a dice roll, round it down to an [[INT]]. Add 1 to the maximum number with [[INT]].
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* The random sequence is 2 ^ 24 or 16,777,216 entries long, which can allow repeated patterns in some procedures.
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* Formulas for the [[INT|Integer]] or [[CINT|Closest Integer]] of ANY number range from ''min%''(lowest value) to ''max%''(greatest value):
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::* Using [[INT]]: randNum% = INT(RND * (max% - min% + 1)) + min%
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::* Using [[CINT]]: randNum% = CINT(RND * (max% - min%)) + min%
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* Use [[RANDOMIZE]] [[TIMER]] for different random number results each time a program is run.
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* [[RUN]] should reset the [[RANDOMIZE]] sequence to the starting [[RND]] function value.(Not yet in QB64)
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''Example 1:'' Generating a random integer value between 1 and 6 (inclusive) using INT.
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{{CodeStart}}
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dice% = {{Cl|INT}}({{Cl|RND}} * 6) + 1 '' '' 'add one as INT value never reaches 6
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{{CodeEnd}}
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''Example 2:'' Using uniform random numbers to create random numbers with a gaussian distribution ([http://en.wikipedia.org/wiki/Marsaglia_polar_method| Marsaglia's polar method]).
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{{CodeStart}} '' ''
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{{Cl|DO}}
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u! = {{Cl|RND}} * 2 - 1
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v! = {{Cl|RND}} * 2 - 1
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s! = u! * u! + v! * v!
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{{Cl|LOOP}} {{Cl|WHILE}} s! >= 1 {{Cl|OR}} s! = 0
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s! = SQR(-2 * {{Cl|LOG}}(s!) / s!) * 0.5
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u! = u! * s!
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v! = v! * s! '' ''
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{{CodeEnd}}
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:''Explanation:'' Values ''u!'' and ''v!'' are now two independent random numbers with gaussian distribution, centered at 0.
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''Example 3:'' Random flashes from an explosion
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{{CodeStart}} '' ''
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{{Cl|SCREEN}} {{Cl|_NEWIMAGE}}(640, 480, 32)
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{{Cl|RANDOMIZE}} {{Cl|TIMER}}
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BC = 120 ' BALL COUNT
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{{Cl|DIM}} ballx(1 {{Cl|TO}} BC)
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{{Cl|DIM}} bally(1 {{Cl|TO}} BC)
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{{Cl|DIM}} velx(1 {{Cl|TO}} BC)
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{{Cl|DIM}} vely(1 {{Cl|TO}} BC)
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{{Cl|DIM}} bsize(1 {{Cl|TO}} BC)
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Y = {{Cl|INT}}({{Cl|RND}} * (400 - 100 + 1)) + 100
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X0 = 325
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Y0 = 300
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Tmax = 150
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DO
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{{Cl|FOR...NEXT|FOR}} p = 1 {{Cl|TO}} BC
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T = {{Cl|INT}}({{Cl|RND}} * (Tmax - 50 + 1)) + 50
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X = {{Cl|INT}}({{Cl|RND}} * (1000 + 500 + 1)) - 500
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velx(p) = (X - X0) / T ' calculate velocity based on flight time
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vely(p) = -1 * (Y - .05 * (T ^ 2 + 20 * Y0)) / (T) ' verticle velocity
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{{Cl|NEXT}} p
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{{Cl|FOR...NEXT|FOR}} w = 1 {{Cl|TO}} BC
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bsize(w) = {{Cl|INT}}({{Cl|RND}} * (10 - 0 + 1)) + 0 'size
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{{Cl|NEXT}} w
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{{Cl|FOR...NEXT|FOR}} J = 1 {{Cl|TO}} Tmax
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{{Cl|_LIMIT}} 60
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{{Cl|CLS}}
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'{{Cl|FOR...NEXT|FOR}} i = 0 {{Cl|TO}} 255 {{Cl|STEP}} .5
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'{{Cl|CIRCLE}} (X0, Y0), i, {{Cl|_RGB}}(255 - i, 0, 0), 0, 3.147
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' {{Cl|NEXT}} i
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R = {{Cl|INT}}({{Cl|RND}} * (25 - 20 + 1)) + 20 'random glimmer
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{{Cl|FOR...NEXT|FOR}} z = 1 {{Cl|TO}} BC
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ballx(z) = X0 + velx(z) * J
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bally(z) = Y0 - vely(z) * J + .5 * .1 * J ^ 2
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{{Cl|NEXT}} z
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{{Cl|FOR...NEXT|FOR}} d = 1 {{Cl|TO}} BC
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RCOL = {{Cl|INT}}({{Cl|RND}} * (255 - 0 + 1)) 'color
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{{Cl|FOR...NEXT|FOR}} i = 0 {{Cl|TO}} bsize(d) + 1 {{Cl|STEP}} .4 'draw balls
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{{Cl|CIRCLE}} (ballx(d), bally(d)), i, {{Cl|_RGBA}}(255, RCOL - (R * i), RCOL - R * i, 255)
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{{Cl|NEXT}} i
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{{Cl|NEXT}} d
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{{Cl|_DISPLAY}}
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{{Cl|NEXT}} J
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{{Cl|LOOP}} {{Cl|UNTIL}} {{Cl|INKEY$}} <> "" '' ''
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{{CodeEnd}} {{small|Code by Falcon}}
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{{PageSeeAlso}}
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* [[RANDOMIZE]], [[TIMER]]
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* [[INT]], [[CINT]], [[FIX]]
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{{PageNavigation}}
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<
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