如何读取数组中的字符输入？

Question

I am writing a program that consists of designing a multiple choice test grader. I declared an array to store the responses. The issue I'm having is that, I don't know how to read each user input (char) to see whether it's correct or not. The code I have, is just a placeholder. I was unable to figure out what to do. This is a snippet of my code:

for (int a = 0 ; a < response.length ; a++)
{
    System.out.print((a + 1) + ": ");
    Scanner s = new Scanner(System.in);
    response [a] = System.in.read();
    while (response [a] < 'A' || response [a] > 'D')
    {
        System.out.println ("Invalid input. Enter answers with A, B, C, or D only!");
        response [a] = System.in.read();
    }
}

Answer 1

I am not entirely sure of what you are trying to achieve so I am going to make a few assumptions for my answer:

The user hits the enter key after each answer which seems natural to me if this is a multiple choice test.

You will know the correct answer and simply need to check that the input is correct.

char [] correctAnswers = {'A', 'B', 'C', 'A'};
Scanner in = new Scanner(System.in);

for(int i = 0; i < correctAnswers; i ++){
    System.out.println("Please input answer:");
    String valueString = in.nextLine().toUpperCase();
    if(valueString.length() != 1){
        System.out.println("Answer invalid. Please only type one character");
        i--;
    } else {
        char answer = valueString.charAt(0);
        if(correctAnswers[i] == answer)
            System.out.println("Correct");
        else
            System.out.println("Wrong");
    }
}

This sample should do the trick.

Alternative

If the user is going to enter all of his answers and then hit enter you can access each character as follows:

char [] correctAnswers = {'A', 'B', 'C', 'A'};
Scanner in = new Scanner(System.in);
System.out.println("Please input " + correctAnswers.length + " answer(s):");
String answerString = in.nextLine().toUpperCase();

if(answerString.length() != correctAnswers.length){
    System.out.println("Incorrect number of answers entered");
} else {
    for(int i = 0; i < answerString.length; i ++){
        if(correctAnswers[i] == answerString.charAt(i)){
            System.out.println("Answer " + (i + 1) + " Correct");
        } else {
            System.out.println("Answer " + (i + 1) + " Wrong");
        }
        count ++;
    }
}

Answer 2

I am not clear about how you are planning to read the input but if you want user to enter the input for each question's answer you can modify the code as below

    for (int a = 0 ; a < response.length ; a++)
        {
            System.out.print((a + 1) + ": ");
            Scanner s = new Scanner(System.in);
            response [a] = s.next();
            while (response [a] < 'A' || response [a] > 'D')
            {
                System.out.println ("Invalid input. Enter answers with A, B, C, or D only!");
                response [a] = s.next().charAt(0);
            }
        }

s.next() takes input as a string so you may need to take the first char out as you are trying to do in the loop.

If you are planning to read input from some file than the reading process would be different, you can look up for that.