random() error in Turbo C++

[Karl Heuer]

In article <118662 at linus.mitre.org> jrv at sdimax2.mitre.org (VanZandt) writes:
>     #define random(n) ((int)((long)rand()*(n))/((long)RAND_MAX+1))
>p.s.  Note that the common device of using rand()%n is guaranteed to
>yield a number in the range 0...n-1, but the probabilities are not uniform.

This is equally true of your version (proof: there are RAND_MAX+1 equally
likely outcomes but n possible results); only the particular "hot" values have
been redistributed.  If it's important, here is a correct algorithm.
	#include <stdlib.h>
	int random(int n) {
	    register int r;
	    do r = rand() / ((RAND_MAX + 1UL) / n); while (r >= n);
	    return (r);
	}

Karl W. Z. Heuer (karl at kelp.ima.isc.com or ima!kelp!karl), The Walking Lint