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	== Notes ==		== Notes ==
	To synchronize rand() on different computers, the function [[rand_seed]]() can be used.		To synchronize rand() on different computers, the function [[rand_seed]]() can be used.
		+
		+	Rand() is not a very good function on itself. To counter this, the following ''rand2()'' can be used:
		+	<pre>
		+	#define RAND_MAX 32767
		+	#define DRAND_RANGE (1.0/((RAND_MAX + 1)*(RAND_MAX + 1)))
		+	#define irand(x) ((unsigned int) ((x) * drand ()))
		+	Function float drand ()
		+	Private
		+	float f;
		+	Begin
		+	Repeat
		+	f = (rand (0,RAND_MAX) * (RAND_MAX + 1.0)
		+	+ rand (0,RAND_MAX)) * DRAND_RANGE;
		+	Until (f < 1); /* Round off */
		+	return f;
		+	End
		+	Function int rand2(int lowerlimit, int upperlimit)
		+	Begin
		+	return (lowerlimit+irand(upperlimit-lowerlimit+1));
		+	End
		+	</pre>
		+	To understand this code, one can read [http://www.azillionmonkeys.com/qed/random.html its source].

---

Revision as of 03:42, 10 January 2008

Contents 1 Definition 2 Parameters 3 Returns 4 Notes

Definition

INT rand ( <INT lowerlimit> , <INT upperlimit> )

Returns a random number, ranging from a certain lower limit to a certain upper limit. The limits are within the range.

Make sure the difference between lowerlimit and upperlimit does not exceed 32767 (2^15).

Parameters

INT lowerlimit	- The lower limit for the random value.
INT upperlimit	- The upper limit for the random value.

Returns

INT : A random value: lowerlimit <= result <= upperlimit

Notes

To synchronize rand() on different computers, the function rand_seed() can be used.

Rand() is not a very good function on itself. To counter this, the following rand2() can be used:

#define RAND_MAX 32767
#define DRAND_RANGE (1.0/((RAND_MAX + 1)*(RAND_MAX + 1)))
#define irand(x) ((unsigned int) ((x) * drand ()))
Function float drand ()
Private
    float f;
Begin
    Repeat
       f = (rand (0,RAND_MAX) * (RAND_MAX + 1.0)
          + rand (0,RAND_MAX)) * DRAND_RANGE;
    Until (f < 1); /* Round off */
    return f;
End
Function int rand2(int lowerlimit, int upperlimit)
Begin
    return (lowerlimit+irand(upperlimit-lowerlimit+1));
End

To understand this code, one can read its source.