Generate Random numbers in array, add them together and store the answers in array

Question

I am new to Java and trying to solve the problem below

So this is my story: Program generates 20 numbers up to 100 and stores every number in array. Once generated the program has to add two numbers and stores the answer in array.. Example

randomNumber[0]+randomNumber[1]=answer[0]
randomNumber[2]+randomNumber[3]=answer[1]
randomNumber[4]+randomNumber[5]=answer[2]

etc..

Once done I check user input with answers and count the correct answers.

The problem is: I can't figure out how to add two numbers together and store it in Array. It seems easy but I am not experienced enough :)

Currently I am stuck here, I would really appreciate if someone could explain or help me how to solve this problem.

public class gNumber {
    private final int[] num = new int[20]; // array of randomly generated numbers
    private int[] answers; // array of correct answers and UserAnswers
    private final int[] userAnswers = new int[10];
    private int numOfCorrect = 0;

    // Accessor to get the randomly generated number
    int getNumbers(final int n) {
        return num[n];
    }

    int numOfCorrectAnswers() {
        return numOfCorrect;
    }

    // Mutator to store store user input
    void setUsrAnswers(final int _index, final int answer) {
        userAnswers[_index] = answer;
    }

    // Method to generate random 20 numbers
    public void RandomN() {

        for (int i = 0; i < num.length; i++) {
            final int randomNum = (int) (Math.random() * 100);
            num[i] = randomNum;
            final int a = num[i];
            // int b =num[i];
            answers[i] = a + a;
            System.out.println(i + ")" + num[i] + answers[i]);
        }

    }

    // method to add two numbers and store in in answers array
    public void add(int arg1, int arg2) {
        int b = 0;
        while (b < 10) {
            arg1 = num[b];
            arg2 = num[b + 1];
            answers[b] = arg1 + arg2;

            System.out.println(answers[b]);
            b = b + 1;
        }
    }

    // method to check user answers
    public void usrInput(final int usrAnwer) {
        for (final int num : answers) {
            if (num == usrAnwer) {
                numOfCorrect++;
            }
        }

    }
}

Answer 1

Sounds simple enough

int b = 0;
while ( b < 20 ) {
    answers[b/2] = num[b] + num[b+1];
    b = b + 2;
}

Answer 2

A solution quite simply:

int N = 20; //20 Random numbers
int[] randomNumber = new int[N];
int[] answer = new int[N/2];

//Generate random numbers of size N
for (int i = 0; i < N; i++) {
    randomNumber = generateRandom(0, 100);
}

//populate answers
for (int i = 0; i < answer.length; i++) {
    answer[i] = randomNumber[i*2] + randomNumber[i*2 + 1];
}

//Generate a random number from [min, max]
private int generateRandom(int min, int max) {
    return min + (int)(Math.random() * ((max - min) + 1));
}

The explanations are on the comments. :-)

Answer 3

You need to step through the num array by 2 when adding up answers:

public void add(int arg1, int arg2) {
    int b = 0;
    while (b < 10) {
        arg1 = num[2*b];
        arg2 = num[2*b + 1];
        answers[b] = arg1 + arg2;

        System.out.println(answers[b]);
        b = b + 1;
    }
}

Answer 4

So, answers will have 10 items, just like userAnswers .

You can therefore do, first:

answers = new int[10]

Then you want answers[0] = num[0] + num[1] . The easiest way would be to go through num two at a time and add the values to answers . So:

int ai = 0
for(int i=0; i<20; i+=2)
    answers[ai++] = num[i] + num[i+1]

Of course, you don't need to keep a reference to ai (answer index). You could do instead:

for(int i=0; i<20; i+=2)
    answers[i/2] = num[i] + num[i+1]