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-->

pwnable.kr-balckjack-Writeup

该题的代码奇长无比（788行）但题挺容易，并且比较有意思

首先从提供的网址https://cboard.cprogramming.com/c-programming/114023-simple-blackjack-program.html查看该题用到的代码如下：

 // Programmer: Vladislav Shulman

 // Final Project

 // Blackjack

 // Feel free to use any and all parts of this program and claim it as your own work

 //FINAL DRAFT

 #include <stdlib.h>

 #include <stdio.h>

 #include <math.h>

 #include <time.h>                //Used for srand((unsigned) time(NULL)) command

 #include <process.h>             //Used for system("cls") command

 #define spade 06                 //Used to print spade symbol

 #define club 05                  //Used to print club symbol

 #define diamond 04               //Used to print diamond symbol

 #define heart 03                 //Used to print heart symbol

 #define RESULTS "Blackjack.txt"  //File name is Blackjack

 //Global Variables

 int k;

 int l;

 int d;

 int won;

 int loss;

 int cash = ;

 int bet;

 int random_card;

 int player_total=;

 int dealer_total;

 //Function Prototypes

 int clubcard();      //Displays Club Card Image

 int diamondcard();   //Displays Diamond Card Image

 int heartcard();     //Displays Heart Card Image

 int spadecard();     //Displays Spade Card Image

 int randcard();      //Generates random card

 int betting();       //Asks user amount to bet

 void asktitle();     //Asks user to continue

 void rules();        //Prints "Rules of Vlad's Blackjack" menu

 void play();         //Plays game

 void dealer();       //Function to play for dealer AI

 void stay();         //Function for when user selects 'Stay'

 void cash_test();    //Test for if user has cash remaining in purse

 void askover();      //Asks if user wants to continue playing

 void fileresults();  //Prints results into Blackjack.txt file in program directory

 //Main Function

 int main(void)

 {

     int choice1;

     printf("\n");

     printf("\n");

     printf("\n");

     printf("\n              222                111                            ");

     printf("\n            222 222            11111                              ");

     printf("\n           222   222          11 111                            ");

     printf("\n                222              111                               ");

     printf("\n               222               111                           ");

     printf("\n");

     printf("\n%c%c%c%c%c     %c%c            %c%c         %c%c%c%c%c    %c    %c                ", club, club, club, club, club, spade, spade, diamond, diamond, heart, heart, heart, heart, heart, club, club);

     printf("\n%c    %c    %c%c           %c  %c       %c     %c   %c   %c              ", club, club, spade, spade, diamond, diamond, heart, heart, club, club);

     printf("\n%c    %c    %c%c          %c    %c     %c          %c  %c               ", club, club, spade, spade, diamond, diamond, heart, club, club);

     printf("\n%c%c%c%c%c     %c%c          %c %c%c %c     %c          %c %c              ", club, club, club, club, club, spade, spade, diamond, diamond, diamond, diamond, heart, club, club);

     printf("\n%c    %c    %c%c         %c %c%c%c%c %c    %c          %c%c %c             ", club, club, spade, spade, diamond, diamond, diamond, diamond, diamond, diamond, heart, club, club, club);

     printf("\n%c     %c   %c%c         %c      %c    %c          %c   %c               ", club, club, spade, spade, diamond, diamond, heart, club, club);

     printf("\n%c     %c   %c%c        %c        %c    %c     %c   %c    %c             ", club, club, spade, spade, diamond, diamond, heart, heart, club, club);

     printf("\n%c%c%c%c%c%c    %c%c%c%c%c%c%c   %c        %c     %c%c%c%c%c    %c     %c            ", club, club, club, club, club, club, spade, spade, spade, spade, spade, spade, spade, diamond, diamond, heart, heart, heart, heart, heart, club, club);

     printf("\n");

     printf("\n                        21                                   ");

     printf("\n     %c%c%c%c%c%c%c%c      %c%c         %c%c%c%c%c    %c    %c                ", diamond, diamond, diamond, diamond, diamond, diamond, diamond, diamond, heart, heart, club, club, club, club, club, spade, spade);

     printf("\n        %c%c        %c  %c       %c     %c   %c   %c              ", diamond, diamond, heart, heart, club, club, spade, spade);

     printf("\n        %c%c       %c    %c     %c          %c  %c               ", diamond, diamond, heart, heart, club, spade, spade);

     printf("\n        %c%c       %c %c%c %c     %c          %c %c              ", diamond, diamond, heart, heart, heart, heart, club, spade, spade);

     printf("\n        %c%c      %c %c%c%c%c %c    %c          %c%c %c             ", diamond, diamond, heart, heart, heart, heart, heart, heart, club, spade, spade, spade);

     printf("\n        %c%c      %c      %c    %c          %c   %c               ", diamond, diamond, heart, heart, club, spade, spade);

     printf("\n     %c  %c%c     %c        %c    %c     %c   %c    %c             ", diamond, diamond, diamond, heart, heart, club, spade, spade);

     printf("\n      %c%c%c      %c        %c     %c%c%c%c%c    %c     %c            ", diamond, diamond, diamond, heart, heart, club, club, club, club, club, spade, spade);

     printf("\n");

     printf("\n         222                     111                         ");

     printf("\n        222                      111                         ");

     printf("\n       222                       111                         ");

     printf("\n      222222222222222      111111111111111                       ");

     printf("\n      2222222222222222    11111111111111111                         ");

     printf("\n");

     printf("\n");

     asktitle();

     printf("\n");

     printf("\n");

     system("pause");

     return();

 } //end program

 void asktitle() // Function for asking player if they want to continue

 {

     char choice1;

     int choice2;

      printf("\n                 Are You Ready?");

      printf("\n                ----------------");

      printf("\n                      (Y/N)\n                        ");

      scanf("\n%c",&choice1);

     while((choice1!='Y') && (choice1!='y') && (choice1!='N') && (choice1!='n')) // If invalid choice entered

     {

         printf("\n");

         printf("Incorrect Choice. Please Enter Y for Yes or N for No.\n");

         scanf("%c",&choice1);

     }

     if((choice1 == 'Y') || (choice1 == 'y')) // If yes, continue. Prints menu.

     {

             system("cls");

             printf("\nEnter 1 to Begin the Greatest Game Ever Played.");

             printf("\nEnter 2 to See a Complete Listing of Rules.");

             printf("\nEnter 3 to Exit Game. (Not Recommended)");

             printf("\nChoice: ");

             scanf("%d", &choice2); // Prompts user for choice

             if((choice2<) || (choice2>)) // If invalid choice entered

             {

                 printf("\nIncorrect Choice. Please enter 1, 2 or 3\n");

                 scanf("%d", &choice2);

             }

             switch(choice2) // Switch case for different choices

             {

                 case : // Case to begin game

                    system("cls");

                    play();

                    break;

                 case : // Case to see rules

                    system("cls");

                    rules();

                    break;

                 case : // Case to exit game

                    printf("\nYour day could have been perfect.");

                    printf("\nHave an almost perfect day!\n\n");

                    system("pause");

                    exit();

                    break;

                 default:

                    printf("\nInvalid Input");

             } // End switch case

     } // End if loop

     else if((choice1 == 'N') || (choice1 == 'n')) // If no, exit program

     {

         printf("\nYour day could have been perfect.");

         printf("\nHave an almost perfect day!\n\n");

         system("pause");

         exit();

     }

     return;

 } // End function

 void rules() //Prints "Rules of Vlad's Blackjack" list

 {

      char choice1;

      int choice2;

      printf("\n           RULES of VLAD's BLACKJACK");

      printf("\n          ---------------------------");

      printf("\nI.");

      printf("\n     Thou shalt not question the odds of this game.");

      printf("\n      %c This program generates cards at random.", spade);

      printf("\n      %c If you keep losing, you are very unlucky!\n", diamond);

      printf("\nII.");

      printf("\n     Each card has a value.");

      printf("\n      %c Number cards 1 to 10 hold a value of their number.", spade);

      printf("\n      %c J, Q, and K cards hold a value of 10.", diamond);

      printf("\n      %c Ace cards hold a value of 11", club);

      printf("\n     The goal of this game is to reach a card value total of 21.\n");

      printf("\nIII.");

      printf("\n     After the dealing of the first two cards, YOU must decide whether to HIT or STAY.");

      printf("\n      %c Staying will keep you safe, hitting will add a card.", spade);

      printf("\n     Because you are competing against the dealer, you must beat his hand.");

      printf("\n     BUT BEWARE!.");

      printf("\n      %c If your total goes over 21, you will LOSE!.", diamond);

      printf("\n     But the world is not over, because you can always play again.\n");

      printf("\n%c%c%c YOUR RESULTS ARE RECORDED AND FOUND IN SAME FOLDER AS PROGRAM %c%c%c\n", spade, heart, club, club, heart, spade);

      printf("\nWould you like to go the previous screen? (I will not take NO for an answer)");

      printf("\n                  (Y/N)\n                    ");

      scanf("\n%c",&choice1);

      while((choice1!='Y') && (choice1!='y') && (choice1!='N') && (choice1!='n')) // If invalid choice entered

     {

         printf("\n");

         printf("Incorrect Choice. Please Enter Y for Yes or N for No.\n");

         scanf("%c",&choice1);

     }

     if((choice1 == 'Y') || (choice1 == 'y')) // If yes, continue. Prints menu.

     {

             system("cls");

             asktitle();

     } // End if loop

     else if((choice1 == 'N') || (choice1 == 'n')) // If no, convinces user to enter yes

     {

         system("cls");

         printf("\n                 I told you so.\n");

         asktitle();

     }

     return;

 } // End function

 int clubcard() //Displays Club Card Image

 {

     srand((unsigned) time(NULL)); //Generates random seed for rand() function

     k=rand()%+;

     if(k<=) //If random number is 9 or less, print card with that number

     {

     //Club Card

     printf("-------\n");

     printf("|%c    |\n", club);

     printf("|  %d  |\n", k);

     printf("|    %c|\n", club);

     printf("-------\n");

     }

     if(k==) //If random number is 10, print card with J (Jack) on face

     {

     //Club Card

     printf("-------\n");

     printf("|%c    |\n", club);

     printf("|  J  |\n");

     printf("|    %c|\n", club);

     printf("-------\n");

     }

     if(k==) //If random number is 11, print card with A (Ace) on face

     {

     //Club Card

     printf("-------\n");

     printf("|%c    |\n", club);

     printf("|  A  |\n");

     printf("|    %c|\n", club);

     printf("-------\n");

     if(player_total<=) //If random number is Ace, change value to 11 or 1 depending on dealer total

          {

              k=;

          }

          else

          {

              k=;

          }

     }

     if(k==) //If random number is 12, print card with Q (Queen) on face

     {

     //Club Card

     printf("-------\n");

     printf("|%c    |\n", club);

     printf("|  Q  |\n");

     printf("|    %c|\n", club);

     printf("-------\n");

     k=; //Set card value to 10

     }

     if(k==) //If random number is 13, print card with K (King) on face

     {

     //Club Card

     printf("-------\n");

     printf("|%c    |\n", club);

     printf("|  K  |\n");

     printf("|    %c|\n", club);

     printf("-------\n");

     k=; //Set card value to 10

     }

     return k;

 }// End function

 int diamondcard() //Displays Diamond Card Image

 {

     srand((unsigned) time(NULL)); //Generates random seed for rand() function

     k=rand()%+;

     if(k<=) //If random number is 9 or less, print card with that number

     {

     //Diamond Card

     printf("-------\n");

     printf("|%c    |\n", diamond);

     printf("|  %d  |\n", k);

     printf("|    %c|\n", diamond);

     printf("-------\n");

     }

     if(k==) //If random number is 10, print card with J (Jack) on face

     {

     //Diamond Card

     printf("-------\n");

     printf("|%c    |\n", diamond);

     printf("|  J  |\n");

     printf("|    %c|\n", diamond);

     printf("-------\n");

     }

     if(k==) //If random number is 11, print card with A (Ace) on face

     {

     //Diamond Card

     printf("-------\n");

     printf("|%c    |\n", diamond);

     printf("|  A  |\n");

     printf("|    %c|\n", diamond);

     printf("-------\n");

     if(player_total<=) //If random number is Ace, change value to 11 or 1 depending on dealer total

          {

              k=;

          }

          else

          {

              k=;

          }

     }

     if(k==) //If random number is 12, print card with Q (Queen) on face

     {

     //Diamond Card

     printf("-------\n");

     printf("|%c    |\n", diamond);

     printf("|  Q  |\n");

     printf("|    %c|\n", diamond);

     printf("-------\n");

     k=; //Set card value to 10

     }

     if(k==) //If random number is 13, print card with K (King) on face

     {

     //Diamond Card

     printf("-------\n");

     printf("|%c    |\n", diamond);

     printf("|  K  |\n");

     printf("|    %c|\n", diamond);

     printf("-------\n");

     k=; //Set card value to 10

     }

     return k;

 }// End function

 int heartcard() //Displays Heart Card Image

 {

     srand((unsigned) time(NULL)); //Generates random seed for rand() function

     k=rand()%+;

     if(k<=) //If random number is 9 or less, print card with that number

     {

     //Heart Card

     printf("-------\n");

     printf("|%c    |\n", heart);

     printf("|  %d  |\n", k);

     printf("|    %c|\n", heart);

     printf("-------\n");

     }

     if(k==) //If random number is 10, print card with J (Jack) on face

     {

     //Heart Card

     printf("-------\n");

     printf("|%c    |\n", heart);

     printf("|  J  |\n");

     printf("|    %c|\n", heart);

     printf("-------\n");

     }

     if(k==) //If random number is 11, print card with A (Ace) on face

     {

     //Heart Card

     printf("-------\n");

     printf("|%c    |\n", heart);

     printf("|  A  |\n");

     printf("|    %c|\n", heart);

     printf("-------\n");

     if(player_total<=) //If random number is Ace, change value to 11 or 1 depending on dealer total

          {

              k=;

          }

          else

          {

              k=;

          }

     }

     if(k==) //If random number is 12, print card with Q (Queen) on face

     {

     //Heart Card

     printf("-------\n");

     printf("|%c    |\n", heart);

     printf("|  Q  |\n");

     printf("|    %c|\n", heart);

     printf("-------\n");

     k=; //Set card value to 10

     }

     if(k==) //If random number is 13, print card with K (King) on face

     {

     //Heart Card

     printf("-------\n");

     printf("|%c    |\n", heart);

     printf("|  K  |\n");

     printf("|    %c|\n", heart);

     printf("-------\n");

     k=; //Set card value to 10

     }

     return k;

 } // End Function

 int spadecard() //Displays Spade Card Image

 {

     srand((unsigned) time(NULL)); //Generates random seed for rand() function

     k=rand()%+;

     if(k<=) //If random number is 9 or less, print card with that number

     {

     //Spade Card

     printf("-------\n");

     printf("|%c    |\n", spade);

     printf("|  %d  |\n", k);

     printf("|    %c|\n", spade);

     printf("-------\n");

     }

     if(k==) //If random number is 10, print card with J (Jack) on face

     {

     //Spade Card

     printf("-------\n");

     printf("|%c    |\n", spade);

     printf("|  J  |\n");

     printf("|    %c|\n", spade);

     printf("-------\n");

     }

     if(k==) //If random number is 11, print card with A (Ace) on face

     {

     //Spade Card

     printf("-------\n");

     printf("|%c    |\n", spade);

     printf("|  A  |\n");

     printf("|    %c|\n", spade);

     printf("-------\n");

     if(player_total<=) //If random number is Ace, change value to 11 or 1 depending on dealer total

          {

              k=;

          }

          else

          {

              k=;

          }

     }

     if(k==) //If random number is 12, print card with Q (Queen) on face

     {

     //Spade Card

     printf("-------\n");

     printf("|%c    |\n", spade);

     printf("|  Q  |\n");

     printf("|    %c|\n", spade);

     printf("-------\n");

     k=; //Set card value to 10

     }

     if(k==) //If random number is 13, print card with K (King) on face

     {

     //Spade Card

     printf("-------\n");

     printf("|%c    |\n", spade);

     printf("|  K  |\n");

     printf("|    %c|\n", spade);

     printf("-------\n");

     k=; //Set card value to 10

     }

     return k;

 } // End Function

 int randcard() //Generates random card

 {

      srand((unsigned) time(NULL)); //Generates random seed for rand() function

      random_card = rand()%+;

      if(random_card==)

      {

          clubcard();

          l=k;

      }

      if(random_card==)

      {

          diamondcard();

          l=k;

      }

      if(random_card==)

      {

          heartcard();

          l=k;

      }

      if(random_card==)

      {

          spadecard();

          l=k;

      }

      return l;

 } // End Function   

 void play() //Plays game

 {

      int p=; // holds value of player_total

      int i=; // counter for asking user to hold or stay (aka game turns)

      char choice3;

      cash = cash;

      cash_test();

      printf("\nCash: $%d\n",cash); //Prints amount of cash user has

      randcard(); //Generates random card

      player_total = p + l; //Computes player total

      p = player_total;

      printf("\nYour Total is %d\n", p); //Prints player total

      dealer(); //Computes and prints dealer total

      betting(); //Prompts user to enter bet amount

      while(i<=) //While loop used to keep asking user to hit or stay at most twenty-one times

                   //  because there is a chance user can generate twenty-one consecutive 1's

      {

          if(p==) //If user total is 21, win

          {

              printf("\nUnbelievable! You Win!\n");

              won = won+;

              cash = cash+bet;

              printf("\nYou have %d Wins and %d Losses. Awesome!\n", won, loss);

              dealer_total=;

              askover();

          }

          if(p>) //If player total is over 21, loss

          {

              printf("\nWoah Buddy, You Went WAY over.\n");

              loss = loss+;

              cash = cash - bet;

              printf("\nYou have %d Wins and %d Losses. Awesome!\n", won, loss);

              dealer_total=;

              askover();

          }

          if(p<=) //If player total is less than 21, ask to hit or stay

          {

              printf("\n\nWould You Like to Hit or Stay?");

              scanf("%c", &choice3);

              while((choice3!='H') && (choice3!='h') && (choice3!='S') && (choice3!='s')) // If invalid choice entered

              {

                  printf("\n");

                  printf("Please Enter H to Hit or S to Stay.\n");

                  scanf("%c",&choice3);

              }

              if((choice3=='H') || (choice3=='h')) // If Hit, continues

              {

                  randcard();

                  player_total = p + l;

                  p = player_total;

                  printf("\nYour Total is %d\n", p);

                  dealer();

                   if(dealer_total==) //Is dealer total is 21, loss

                   {

                       printf("\nDealer Has the Better Hand. You Lose.\n");

                       loss = loss+;

                       cash = cash - bet;

                       printf("\nYou have %d Wins and %d Losses. Awesome!\n", won, loss);

                       dealer_total=;

                       askover();

                   } 

                   if(dealer_total>) //If dealer total is over 21, win

                   {

                       printf("\nDealer Has Went Over!. You Win!\n");

                       won = won+;

                       cash = cash+bet;

                       printf("\nYou have %d Wins and %d Losses. Awesome!\n", won, loss);

                       dealer_total=;

                       askover();

                   }

              }

              if((choice3=='S') || (choice3=='s')) // If Stay, does not continue

              {

                 printf("\nYou Have Chosen to Stay at %d. Wise Decision!\n", player_total);

                 stay();

              }

           }

              i++; //While player total and dealer total are less than 21, re-do while loop

      } // End While Loop

 } // End Function

 void dealer() //Function to play for dealer AI

 {

      int z;

      if(dealer_total<)

      {

       srand((unsigned) time(NULL) + ); //Generates random seed for rand() function

       z=rand()%+;

       if(z<=) //If random number generated is 10 or less, keep that value

       {

          d=z;

       }

       if(z>) //If random number generated is more than 11, change value to 10

       {

          d=;

       }

       if(z==) //If random number is 11(Ace), change value to 11 or 1 depending on dealer total

       {

          if(dealer_total<=)

          {

              d=;

          }

          else

          {

              d=;

          }

       }

      dealer_total = dealer_total + d;

      }

      printf("\nThe Dealer Has a Total of %d", dealer_total); //Prints dealer total

 } // End Function 

 void stay() //Function for when user selects 'Stay'

 {

      dealer(); //If stay selected, dealer continues going

      if(dealer_total>=)

      {

       if(player_total>=dealer_total) //If player's total is more than dealer's total, win

       {

          printf("\nUnbelievable! You Win!\n");

          won = won+;

          cash = cash+bet;

          printf("\nYou have %d Wins and %d Losses. Awesome!\n", won, loss);

          dealer_total=;

          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+;

          cash = cash - bet;

          printf("\nYou have %d Wins and %d Losses. Awesome!\n", won, loss);

          dealer_total=;

          askover();

       }

       if(dealer_total>) //If dealer's total is more than 21, win

       {

          printf("\nUnbelievable! You Win!\n");

          won = won+;

          cash = cash+bet;

          printf("\nYou have %d Wins and %d Losses. Awesome!\n", won, loss);

          dealer_total=;

          askover();

       }

      }

      else

      {

          stay();

      }

 } // End Function

 void cash_test() //Test for if user has cash remaining in purse

 {

      if (cash <= ) //Once user has zero remaining cash, game ends and prompts user to play again

      {

         printf("You Are Bankrupt. Game Over");

         cash = ;

         askover();

      }

 } // End Function

 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

 void askover() // Function for asking player if they want to play again

 {

     char choice1;

      printf("\nWould You Like To Play Again?");

      printf("\nPlease Enter Y for Yes or N for No\n");

      scanf("\n%c",&choice1);

     while((choice1!='Y') && (choice1!='y') && (choice1!='N') && (choice1!='n')) // If invalid choice entered

     {

         printf("\n");

         printf("Incorrect Choice. Please Enter Y for Yes or N for No.\n");

         scanf("%c",&choice1);

     }

     if((choice1 == 'Y') || (choice1 == 'y')) // If yes, continue.

     {

             system("cls");

             play();

     }

     else if((choice1 == 'N') || (choice1 == 'n')) // If no, exit program

     {

         fileresults();

         printf("\nBYE!!!!\n\n");

         system("pause");

         exit();

     }

     return;

 } // End function

 void fileresults() //Prints results into Blackjack.txt file in program directory

 {

     FILE *fpresults; //File pointer is fpresults

     fpresults = fopen(RESULTS, "w"); //Creates file and writes into it

     if(fpresults == NULL) // what to do if file missing from directory

     {

                printf("\nError: File Missing\n");

                system("pause");

                exit();

     }

     else

     {

      fprintf(fpresults,"\n\t RESULTS");

      fprintf(fpresults,"\n\t---------\n");

      fprintf(fpresults,"\nYou Have Won %d Times\n", won);

      fprintf(fpresults,"\nYou Have Lost %d Times\n", loss);

      fprintf(fpresults,"\nKeep Playing and Set an All-Time Record!");

     }

      fclose(fpresults);

      return;

 } // End Function

虽然代码足足有近800行，但根据代码的流程逐渐分析，还是能分析出以下信息：

游戏规则
- 玩家在每轮游戏开始之前设置赌资；
- 玩家的任务是通过hit（继续加扑克牌）或者stay（等待）使自己的点数之和等于21；
- 卡片1~10的点数即为相对应的数字，卡片J，Q，K的点数为10，卡片A的点数为11；
- 当自己的点数大于了21，或者自己的点数小于了庄家的点数，玩家输；则要从赌本中减去赌资；
- 当玩家的点数之和等于21时，玩家胜；玩家就从庄家处赚取同赌资金额的金钱；
当玩家的赌本大于1000000时，胜利，即可拿到flag；

由以上分析，首先先到了三种方法作弊（或者相信自己的人品无穷大，可以通过自己的努力能成为百万富翁）：

直接修改赌本为 ≥ 1000000；
通过修改，使自己每局都能获胜，那么需要
在每局结束时动手脚，增加赌本

分析代码，前两种想法没有找到相应的漏洞，
第三种方法，分析betting函数:

 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

可以看出函数对输入的赌资只做了是否小于赌本的判断，那么我们就可以输入一个负的大小合适的赌本（大小合适指不会数据溢出），如-1000000；
那么，如果我们输掉了那一局，我们的赌本就要减负的1000000，就是加正的1000000，就可以拿到flag；

经过几次探索，拿到flag如下：

则flag即为YaY_I_AM_A_MILLIONARE_LOL
2017-2-16 8:16;47

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pwnable.kr-balckjack-Writeup

游戏规则

当玩家的赌本大于1000000时，胜利，即可拿到flag；

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