看了一下游戲規則，玩家和AI一起玩牌，起初有500塊，首先下注，之後每次各自會收到一張隨機的牌（點數1-13），最先達到21點的人贏。每次拿到牌之後，你可以選擇hit（繼續拿牌）或者是stay（不拿）。如果繼續拿了牌之後超過21點，那麼你就輸了。如果你選擇stay，那麼AI可能拿到超過你的點數贏你，或者超過21點輸掉。

我們的目標是每次下注贏到millionare。由於發牌是隨機的，不想一直靠運氣玩下去的話就來審一下程式碼吧。

漏洞位置在下注bet這裡：

int betting() //Asks user amount to bet
{
 printf("\n\nEnter Bet: $");
 scanf("%d", &bet);
 
 if (bet > cash) //If player tries to bet more money than player has
 {
        printf("\nYou cannot bet more money than you have.");
        printf("\nEnter Bet: ");
        scanf("%d", &bet);
        return bet;
 }
 else return bet;
} // End Function
 

如果下注的錢bet超過了你擁有的錢cash，那麼會讓你再輸入一次，再輸入下注的錢的時候居然沒有繼續判斷。

那麼，不管你選擇stay還是選擇hint，輸贏對於cash的修改是一致的，以stay為例，贏了cash+bet。輸了cash-bet。

void stay() //Function for when user selects 'Stay'
{
     dealer(); //If stay selected, dealer continues going
     if(dealer_total>=17)
     {
      if(player_total>=dealer_total) //If player's total is more than dealer's total, win
      {
         printf("\nUnbelievable! You Win!\n");
         won = won+1;
         cash = cash+bet;
         printf("\nYou have %d Wins and %d Losses. Awesome!\n", won, loss);
         dealer_total=0;
         askover();
      }
      if(player_total<dealer_total) //If player's total is less than dealer's total, loss
      {
         printf("\nDealer Has the Better Hand. You Lose.\n");
         loss = loss+1;
         cash = cash - bet;
         printf("\nYou have %d Wins and %d Losses. Awesome!\n", won, loss);
         dealer_total=0;
         askover();
      }
      ...
      
} // End Function
 

那麼cash輸入一個負數，繼續輸，cash=cash-bet。cash輸入一個正數，贏一次，cash=cash+bet。

flag

Cash: $500
-------
|C    |
|  5  |
|    C|
-------

Your Total is 5

The Dealer Has a Total of 8

Enter Bet: $501

You cannot bet more money than you have.
Enter Bet: -10000000


Would You Like to Hit or Stay?
Please Enter H to Hit or S to Stay.
s

You Have Chosen to Stay at 5. Wise Decision!

The Dealer Has a Total of 16
The Dealer Has a Total of 24
Dealer Has the Better Hand. You Lose.

You have 0 Wins and 1 Losses. Awesome!

Would You Like To Play Again?
Please Enter Y for Yes or N for No
y
==================================================
YaY_I_AM_A_MILLIONARE_LOL


Cash: $10000500
-------
|S    |
|  1  |
|    S|
-------

Your Total is 1

The Dealer Has a Total of 9

Enter Bet: $
 

嗯，找漏洞的時候需要明確我們的目標，比如cash>1000000，只看cash相關的程式碼就可以更快一點。