Task

(Given an equal-probability generator of one of the integers 1 to 5
as dice5),   create dice7 that generates a pseudo-random integer from
1 to 7 in equal probability using only dice5 as a source of random
numbers,   and check the distribution for at least one million calls using the function created in   Simple Random Distribution Checker.


Implementation suggestion:
dice7 might call dice5 twice, re-call if four of the 25
combinations are given, otherwise split the other 21 combinations
into 7 groups of three, and return the group index from the rolls.

(Task adapted from an answer here)

int rand5()
{
	int r, rand_max = RAND_MAX - (RAND_MAX % 5);
	while ((r = rand()) >= rand_max);
	return r / (rand_max / 5) + 1;
}
 
int rand5_7()
{
	int r;
	while ((r = rand5() * 5 + rand5()) >= 27);
	return r / 3 - 1;
}
 
int main()
{
	printf(check(rand5, 5, 1000000, .05) ? "flat\n" : "not flat\n");
	printf(check(rand7, 7, 1000000, .05) ? "flat\n" : "not flat\n");
	return 0;
}