#include 
  
   
#include 
   
     #include 
    
      //system(); 这个指令需要用到此头文件 #include 
     
       //toupper要用到 #include 
      
        //在内存管理时用到的头文件 void main() { char letter; // Letter typed by the user printf("Do you want to continue? (Y/N): "); letter = _getch(); // Get the letter letter = toupper(letter); // Convert letter to uppercase while ((letter != 'Y') && (letter != 'N')) { _putch(7); // Beep the speaker letter = _getch(); // Get the letter letter = toupper(letter); // Convert letter to uppercase } printf("\nYour response was %c\n", letter); system("pause"); }