Java

Question

我的目标是从用户那里获得特定的输入（仅限 A、B、C 和 D）。

例如：如果我输入字母 A，if 语句将执行（它不应该）。 do while 也一样。（逻辑错误）

  char[] response = new char[20];
  Scanner k = new Scanner(System.in);

  //Prompts User to fill array with their responses
  for(int i=0; i<response.length; i++) {
       //Input validation
       do {
          System.out.println("Answer "+(i+1)+":");
          response[i] = k.nextLine().charAt(0); 

          if(response[i] != 'A' ||response[i] != 'B' || response[i] != 'C' ||response[i] != 'D')
              System.out.print("Try Again. ");
       }
       while(response[i]!= 'A' ||response[i] != 'B' ||response[i] != 'C' ||response[i] != 'D');
  }

Answer 1

你条件倒退了。当你得到它 A 你会得到

if (false || true || true || true)

这会过去的。

将此更改为：

if(response[i] != 'A' && response[i] != 'B' && response[i] != 'C' && response[i] != 'D')

Answer 2

我会这样写

Scanner in = new Scanner(System.in);
char[] response = new char[20];

//Prompts User to fill array with their responses
for(int i = 0; i < response.length; i++) {
   for (;;) {
       System.out.println("Answer " + (i + 1) + ":");
       response[i] = in.nextLine().charAt(0);
       //Input validation
       if ("ABCD".indexOf(response[i]) >= 0)
           break;
       System.out.print("Please try again, it must be A, B, C or D");
   }
}

你做错的是你需要写

if (!(response[i] == 'A' || response[i] == 'B' || response[i] == 'C' || response[i] != 'D'))

或

if (response[i] != 'A' && response[i] != 'B' && response[i] != 'C' && response[i] != 'D')

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