MontyHall.cpp

/**
 * MontyHall.cpp
 *
 * Example Monty Hall problem simulation.
 * usage: g++ MontyHall.cpp -o MontyHall && ./MontyHall
 *
 * @author Maxamilian Demian
 * @link https://www.maxodev.org
 * @link https://github.com/Maxoplata/MontyHall
 */
#include <iostream>

int main() {
	// The number of times to run for each choice (keep and change will run numberOfRuns times EACH)
	int numberOfRuns = 1000000;

	int keepWins = 0;
	int keepLosses = 0;
	int changeWins = 0;
	int changeLosses = 0;

	// seed rng
	srand(time(NULL));

	// loop numberOfRuns without changing our initial door selection
	for (int i = 0; i < numberOfRuns; i++) {
		// pick a winning door between 1 and 3
		int winningDoor = (rand() % 3) + 1;

		// player selects a random door between 1 and 3
		int playerDoor = (rand() % 3) + 1;

		if (playerDoor == winningDoor) {
			// player chose the winning door
			keepWins++;
		} else {
			// player chose a losing door
			keepLosses++;
		}
	}

	// loop numberOfRuns while changing our initial door selection
	for (int i = 0; i < numberOfRuns; i++) {
		// pick a winning door between 1 and 3
		int winningDoor = (rand() % 3) + 1;

		// player selects a random door between 1 and 3
		int playerDoor = (rand() % 3) + 1;

		if (playerDoor == winningDoor) {
			// player chose the winning door already, count it as a loss as the player will be changing
			changeLosses++;
		} else {
			/* if the player HAS NOT chosen the winning door already and they change, they will win
			 * example:
			 * - player chooses door 1
			 * - winning door is door 3
			 * - host opens door 2 showing a goat
			 * - player switches to door 3 and wins
			 *
			 * every variation of this will win since we have already eliminated the aspect of the player
			 * having already picked the winning door
			 */
			changeWins++;
		}
	}

	printf("Keep Wins/Losses: %d/%d (%f%% wins)\n", keepWins, keepLosses, (((float) keepWins / numberOfRuns) * 100));
	printf("Change Wins/Losses: %d/%d (%f%% wins)\n", changeWins, changeLosses, (((float) changeWins / numberOfRuns) * 100));
}