如何在if / else语句中添加while循环

Question

我正在尝试为此程序添加一个while循环。 到目前为止，它会生成2个随机数，用户必须输入数字的乘积。 现在，用户每次必须重新运行该程序。 目标是让用户继续此操作，直到他们决定通过输入前哨值-1来停止。 我是否应该将while循环放在if语句上方？

  Random random = new Random();
  Scanner scan = new Scanner(System.in);

  final int SENTINEL = -1;
  int number1 = random.nextInt(13);
  int number2 = random.nextInt(13);
  int answer = number1 * number2;

  System.out.print("What is " + number1 + " X " + number2 + "? > ");
  int product = scan.nextInt(); 

  if (product == answer) {
    System.out.println("Correct! " + number1 + " X " + number2 + " = " + answer);
  } else { 
     System.out.println("Wrong " + number1 + " X " + number2 + " = " + answer);
  }

Answer 1

如果希望用户每次获得一个新的随机生成的数字，则while循环应该在生成随机数之前进行。 换一种说法：

Random random = new Random();
Scanner scan = new Scanner(System.in);

final int SENTINEL = -1;
int number1;
int number2;
int product = 0;

while (product != SENTINEL) {
  number1 = random.nextInt(13);
  number2 = random.nextInt(13);
  int answer = number1 * number2;

  System.out.print("What is " + number1 + " X " + number2 + "? > ");
  product = scan.nextInt(); 

  if (product == answer) {
    System.out.println("Correct! " + number1 + " X " + number2 + " = " + answer);
  } else { 
    System.out.println("Wrong " + number1 + " X " + number2 + " = " + answer);
  }
}

通常，while语句应放在要重复的代码的第一部分之前。

Answer 2

像这样：

while(true){
  number1 = random.nextInt(13);
  number2 = random.nextInt(13);
  int answer = number1 * number2;
  System.out.print("What is " + number1 + " X " + number2 + "? > ");
  int product = scan.nextInt(); 

  if(product == SENTINEL){
     System.exit(0);  // you could also use break; here
  }
  if (product == answer) {
    ...
}