c - 为什么这段代码可以在 gcc 6.3.0 上运行，而不能在 4.9.2 上运行？

Question

我有一个类(class)游戏，用于显示二分搜索。该代码在我的 ide(atom) 和 gcc 编译器(gcc 版本 6.3.0 (MinGW.org GCC-6.3.0-1))上编译和运行没有错误。我的教授正在使用 Dev C++，他的编译器是(gcc 4.9.2)。不幸的是，他的版本编译时不会出现错误，但在从普通游戏中获取用户输入时也会失败。我在调试方面不够熟练，无法找出问题所在。感谢任何帮助，并且解释将是令人难以置信的。

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



//--Menu--//
//user input for main menu
int userInput(){
  int var;
  scanf("%d", &var);
  return var;
}
//main menu for the user to decide what version they want to play
void menuMain(){
  printf("------------------------\n");
  printf("Menu\n");
  printf("1 - Normal Game\n");
  printf("2 - Efficency Mode\n");
  printf("3 - Quick Game\n");
  printf("4 - EXIT PROGRAM\n");
  printf("------------------------\n");
};
//good bye message
void menuGoodBye(){
  printf("---------------\n");
  printf("Good Bye!\n");
  printf("---------------\n");
}
//gets the users response and capitalizes it
char responseUser(int guess){
  char y;
  printf("---------------------------------------------\n");
  printf("Is it %d?\n",guess);
  printf("Please respond with Lower (L), Higher (H), or Correct (C).\n");
  scanf("%s",&y);
  y = toupper(y);
  return y;
}

//--Normal Game--//
//instructions for the user Normal Games
void instructions(int min,int max){
  printf("----------------------------------------------------------------------\n");
  printf("Pick a number from %d to %d and I will try and guess it.\n",min, 
  max);
  printf("If your number is lower, respond with a L.\n");
  printf("If your number is higher, respond with a H.\n");
  printf("If I guess correctly, respond with a C.\n");
  printf("----------------------------------------------------------------------\n");
}
//uses binary search for efficient gameplay
int efficentGuesser(int min, int max){
  return (max+min)/2;
}
//uses random numbers with updated minimums and maximums
int gameGuesser(int min, int max){
  int x;
  x=rand()%(max+1-min)+min;
  return x;
}
//the modular switch for the game
void gameSwitch(int (*method)(int, int),int min, int max){
  char response;
  int guess;
  do{
     guess = (*method)(min,max);
     response = responseUser(guess);
     switch (response) {
       case 'L':
         max= guess-1;
       break;
       case 'H':
         min= guess+1;
       break;
       case 'C':
       break;
       default:
       break;
     }
   }while(response != 'C');
}


//--Quick Game--//
//instructions for the quick game
void instructionsQuickGame(int min, int max){
  printf("----------------------------------------------------------------------\n");
  printf("Pick a number from %d to %d and I will try and guess it.\n",min, 
  max);
  printf("----------------------------------------------------------------------\n");
}
//search for a quick game
void quickGame(int (*method)(int, int),int x, int y){
  int input,guess,min,max, trys;
    input= userInput();

    clock_t begin = clock();
    min = x;
    max = y;

  do{
    guess=(*method)(min, max);
    if(input > guess){
      min = guess + 1;
    }else{
      max = guess - 1;
    }
    trys++;
  }while(input != guess);
  clock_t end = clock();

  printf("Wow,That took me %.8f seconds and %d trys!\n",(double)(end - 
  begin) / CLOCKS_PER_SEC,trys);

}

//--Modular Block--//
//basic building block for game, you can import functions modularly
void defaultGame(int (*method)(int, int), void (*s)(), void(*instructions) 
(int, int)){
  int min, max;
  min =0;
  max =100;
  (*instructions)(min,max);
  (*s)((*method),min,max);

}


//the actual code that runs
int main(){
  srand(time(0));
  int response;
  do{
    menuMain();
    response=userInput();
    switch (response){
      case 1:
        //defaultGame(method, what switch, what instructions)
        defaultGame(gameGuesser, gameSwitch, instructions);
      break;
      case 2:
        //defaultGame(method, what switch, what instructions)
        defaultGame(efficentGuesser, gameSwitch,instructions);
      break;
      case 3:
        //defaultGame(method, what switch, what instructions)
        defaultGame(efficentGuesser, quickGame, instructionsQuickGame);
      break;
      case 4:
        menuGoodBye();
      break;
      default:
        printf("Please Pick a number from the menu.\n");
      break;
    }
  }while(response != 4);

  return EXIT_SUCCESS;
}

Answer 1

未定义行为 (UB)

字符； ... scanf("%s",&y); 是未定义的行为，因为 "%s" 指示 scanf() 形成一个字符串 至少一个非空白字符加上附加的空字符。 char y 太小了。 @Eugene Sh.

请考虑以下内容。

scanf(" %c",&y);

<小时/>

其他问题也存在，但以上是一个大问题。