java - 在Java中查找2个数组中匹配元素的数量

Question

我目前正在做一个课本上的练习(不是作业，自学)，给出了多项选择考试的正确答案，我将其命名为answerKey，要求用户输入学生的答案，然后找到用于计算等级的匹配元素。请看看我到目前为止做了什么。我不明白的是 numCount 的行为，以及为什么它不能正确返回。我想要这方面的指导。谢谢!

import java.util.Arrays;
import java.util.Scanner;

public class Drivers_License
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);

        int incorrect = 0;
        double grade = 0.0;
        String input;
        char[] answerKey = {'B', 'D', 'A', 'A', 'C',
                            'A', 'B', 'A', 'C', 'D',
                            'B', 'C', 'D', 'A', 'D',
                            'C', 'C', 'B', 'D', 'A'};
        System.out.println();

        int numCorrect = 0;
        int total = 0;
        char[] responses = new char[20];
        for (int i = 0; i < responses.length; i++) {
            System.out.printf("Enter answer for # %d: ", i+1);
            responses[i] = scan.nextLine().toUpperCase().trim().charAt(0);
            for (int j = 0; j < answerKey.length; j++) {
                if (responses[i] == (answerKey[j])) {
                    System.out.println(responses[i]);
                    numCorrect++; // I don't quite understand
                                  // what is happening here...
                }
            }
        }

        /* Display elements in userAnswers array */
        System.out.println("User answers are below");
        for (int i = 0; i < responses.length; i++) {
            System.out.print(responses[i] + " ");
        }
        System.out.println();
    }


$ java Drivers_License

Enter answer for # 1: a
Enter answer for # 2: b
Enter answer for # 3: c
Enter answer for # 4: d
Enter answer for # 5: a
Enter answer for # 6: b
Enter answer for # 7: c
Enter answer for # 8: d
Enter answer for # 9: a
Enter answer for # 10: b
Enter answer for # 11: c
Enter answer for # 12: d
Enter answer for # 13: a
Enter answer for # 14: b
Enter answer for # 15: c
Enter answer for # 16: d
Enter answer for # 17: a
Enter answer for # 18: b
Enter answer for # 19: c
Enter answer for # 20: d
No. of correct answers: 100
User answers are below
A B C D A B C D A B C D A B C D A B C D 

Answer 1

您正在使用两个 for 循环(一个在另一个循环内)。这些是嵌套的 for 循环。上面代码中发生的情况是，对于第一个数组中的每个索引 i，都会访问第二个数组中的所有 j。

您想要做的是只有一个 for 循环(20 次迭代)并并行访问两个数组中的元素。

    public class Drivers_License
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);

        int incorrect = 0;
        double grade = 0.0;
        String input;
        char[] answerKey = {'B', 'D', 'A', 'A', 'C',
                            'A', 'B', 'A', 'C', 'D',
                            'B', 'C', 'D', 'A', 'D',
                            'C', 'C', 'B', 'D', 'A'};
        System.out.println();

        int total = 0;
        char[] responses = new char[20];
        for (int i = 0; i < responses.length; i++) 
        {
            System.out.printf("Enter answer for # %d: ", i+1);
            responses[i] = scan.nextLine().toUpperCase().trim().charAt(0);

        }

        int numCorrect = 0;
        for (int i = 0; i < responses.length; i++) {
           if (responses[i] == (answerKey[i])) { // Look here
                System.out.println(responses[i]);
                numCorrect++;
            }
        }

        /* Display elements in userAnswers array */
        System.out.println("User answers are below");
        for (int i = 0; i < responses.length; i++) {
            System.out.print(responses[i] + " ");
        }
        System.out.println();
    }