java - 如何使用 'for' 循环来检查输入中的某些数字？

Question

我是java新手，对使用循环也很陌生，到目前为止，我一直在为我的类(class)解决一个问题，制作一个程序来检查用户是否输入随机生成的正确数字的变体，但它说一旦循环开始，就无法找到lotteryNumberString。有关如何修复它的任何提示吗？

    import java.util.Scanner;
    public class Lottery
    {
    public static void main(String[] args)
    {
    Scanner input = new Scanner(System.in);

    for(int i=0; i < 3; i++)
    {
        double lotto = Math.random();
        int lotteryNumberDigit = (int)(lotto*10);

        String lotteryNumberString = Integer.toString(lotteryNumberDigit);

        }



            String firstNumber = lotteryNumberString.substring(0,0);
            String secondNumber = lotteryNumberString.substring(1,1);
            String thirdNumber = lotteryNumberString.substring(2,2);

            String firstTwoWinner = firstNumber + secondNumber;
            String lastTwoWinner = secondNumber + thirdNumber;
            String allNumbersWinner = firstNumber + secondNumber + thirdNumber;

            System.out.println("Please enter your three numbers (e.g. 123): ");

            String userInput = input.next();

             if(userInput.substring(0,2).equals(firstTwoWinner))

        {
            System.out.println("Winner: " + allNumbersWinner );

            System.out.println("Congratulations, the front pair matched.");
        }

        else if (userInput.substring(1,3).equals(lastTwoWinner))
        {
             System.out.println("Winner: " + allNumbersWinner );

             System.out.println("Congratulations, the end pair matched.");
        }

        else if (userInput.equals(allNumbersWinner))
        {
             System.out.println("Winner: " + allNumbersWinner );

             System.out.println("Congratulations, both pairs matched.");
        }

        else
        {
             System.out.println("Winner: " + allNumbersWinner );

             System.out.println("Sorry, no matches. You only had one chance out of 100 to win anyway.");
        }



    }
}

Answer 1

看看这篇文章:http://www.java-made-easy.com/variable-scope.html 。您面临的问题与lotteryNumberString 变量的范围(生命周期)有关。如果您在循环内部声明，则它不存在于循环外部。要解决此问题，请在 for 循环之前声明lotteryNumberString