Program terminates when i try to run it

I have to create a class that asks the user to answer a multiplication problem. It randomly pulls to integers. If the answer is correct it displays a response if its wrong it displays a response and tells them to try again. at the end it displays all the questions with the answers. For some reason when i run the program it automatically terminates but doesnt give me an error. Any help would be appreciated. Thank you

Java Code:

import java.util.ArrayList;
import java.util.Random;
import java.util.Scanner;

//import javax.swing.*;

public class StudentMath {

        private int num[] = new int[2]; // array of numbers for random numbers
        private int ans;
        private boolean right = true;
        private boolean wrong = false;
        private int arr[] = new int[2];
        private ArrayList<String> results = new ArrayList<String>(); // array of random questions
        private String choice;
        Random r = new Random(); //instantize Random
        Scanner sc = new Scanner(System.in);// instantize Scanner
        
        public void generateQuestion() {//Method creates 2 random numbers
                arr[0] = r.nextInt(9);
                arr[1] = r.nextInt(9);
                num = arr;
        }

        public void createQuestion() { //Method creates question using random integers

                while (ans != (num[0] * num[1])) {
                        generateQuestion();
                        do {
                                
                                System.out.print("\nHow much is " + num[0] + " times " + num[1]
                                                + " ? :");
                                ans = sc.nextInt();
                                results.add(num[0] + " times " + num[1] + "=" + num[0] * num[1]);//adds to result array
                                checkAnswer();
                                System.out.print("\nDo you want more questions(y/n) :");
                                sc.nextLine();
                                choice = sc.nextLine();

                        } while (choice.equalsIgnoreCase("y"));
                }
                }
        public void checkAnswer(){ //checks if user input is correct
                                if (ans == (num[0] * num[1]))
                                        createResponse(right);
                                else
                                        createResponse(wrong);                  
        }

        public void createResponse(boolean b) { //generates response if right or wrong answer

                final String[] correct = { "Very good!", "Excellent!", "Nice work!",
                                "Keep up the good work!" };
                final String[] wrong = { "No. Please try again",
                                "Wrong. Try once more", "Don't give up!", "No. Keep trying" };
                int index;

                if (b == true) {
                        index = r.nextInt(correct.length);
                        System.out.print(correct[index]);
                } else {
                        index = r.nextInt(wrong.length);
                        System.out.print(wrong[index]);
                }
        }

        public void printResults() { //prints results of questions asked
                String output = "";
                for (int i = 0; i < results.size(); i++) {
                        String everything = results.get(i).toString();
                        output += everything + "\n";
                }
                System.out.print(output);
                sc.close();
        }

        public static void main(String args[]) {

                StudentMath sm = new StudentMath(); //instantize class StudentMath

                sm.createQuestion();

                sm.printResults();
        }
}