montyhall.c

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

short int reveal(short int firstDoor, short int moneyDoor) {
  short int arr[3] = {0, 1, 2};
  if (firstDoor == moneyDoor) {
    short int newArr[2];
    short int j = 0;
    for (short int i = 0; i < 3; i++) {
      if (i == moneyDoor) continue;
      newArr[j++] = i;
    }
    return newArr[rand() % 2];
  } else
    return 3 - firstDoor - moneyDoor;
}

int main() {
  srand(time(NULL));
  const unsigned int tries = 2500000000;
  static unsigned int stayWins = 0;
  static unsigned int swapWins = 0;

  for (unsigned int i = 0; i < tries; i++) {
    short int moneyDoor = (short int)(rand() % 3);
    short int firstChoice = (short int)(rand() % 3);
    short int revealedDoor = reveal(firstChoice, moneyDoor);
    if (firstChoice == moneyDoor)
      stayWins++;
    else {
      short int swappedDoor = 3 - firstChoice - revealedDoor;
      if (swappedDoor == moneyDoor) swapWins++;
    }
  }
  printf("Swapped wins: %u\nSwap win percent: %f%%\n", swapWins, ((1.0 * swapWins)/tries)*100);
  printf("Stayed wins: %u\nStay win percent: %f%%\n", stayWins, ((1.0 * stayWins)/tries)*100);
  printf("Ratio: %f\n", ((swapWins * 1.0)/stayWins));
  return 0;
}