Test the Monty Hall problem

montyhall.c

#include <stdio.h>
#include <stdlib.h>

#define rand3() ((int)(rand() % 3)+1)

void seedrand()
{
	unsigned int randval;
	FILE *f;

	f = fopen("/dev/random", "r");
	fread(&randval, sizeof(randval), 1, f);
	fclose(f);

	srand(randval);
}

inline bool play()
{
	int car = 0;
	int choice = 0;
	int opened = 0;

	// Assign the car.
	car = rand3();

	// Make the initial choice.
	choice = rand3();

	// Open a door.
	while (opened == 0 || opened == choice || opened == car) {
		opened = rand3();
	}

	// Change our choice.
	if (choice != 1 && opened != 1) {
		choice = 1;
	} else if (choice != 2 && opened != 2) {
		choice = 2;
	} else {
		choice = 3;
	}

	return choice == car;
}

int main()
{
	seedrand();

	int count = 10000000;
	int wins = 0;

	for (int i = 0; i < count; i++) {
		if (play()) {
			wins += 1;
		}
	}

	printf("Won %.4g%%\n", (((double)wins) / count) * 100);

	return 0;
}