Question

According to the probabilities I’ve read about, switching doors should yield ~66% chance to pick the correct door. This code below is what I’ve come up with and it spits out roughly 50% wins instead of the 66% I am expecting. Any help on where I’m going wrong here would be much appreciated.

for (int count = 0; count < 10000; count++)
{
    // Chooses which door contains DAT GRAND PRIZE YO.
    wDoor = rand() % 3 + 1;

    // AI Contestants Door choice
    aiDoor = rand() % 3 + 1;

    // Using oldChoice to ensure same door isn't picked.
    oldChoice = aiDoor;
    // Used in determining what door to open.
    openedDoor = aiDoor;

    // "Open" a door that is not the winning door and not the door chosen by player.
    do
    {
                openedDoor = rand() % 3 + 1;

    }while (openedDoor != wDoor && openedDoor != aiDoor);

    // Select new door between the remaining two.
    do
    {
              aiDoor = rand() % 3 + 1;

    }while (aiDoor != oldChoice && aiDoor != openedDoor);

    // Increment win counter if new door is correct.
    if (aiDoor == wDoor)
    {
               chooseAgain++;
    }

}

Answer 1

Your while conditions are the wrong way round:

while (openedDoor != wDoor && openedDoor != aiDoor)

should be

while (openedDoor == wDoor || openedDoor == aiDoor)

etc.