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