1. package com.example.mathchallenge;
2.  
3. import androidx.appcompat.app.AppCompatActivity;
4. import android.os.Bundle;
5. import android.view.View;
6. import android.widget.Button;
7. import android.widget.EditText;
8. import android.widget.TextView;
9. import java.util.Random;
10.  
11. public class MainActivity extends AppCompatActivity {
12.     int score = 0; //to keep track of the user's score
13.     int num1, num2, answer; //variables to hold the first number, second number, and answer respectively
14.  
15.     @Override
16.     protected void onCreate(Bundle savedInstanceState) {
17.         super.onCreate(savedInstanceState);
18.         setContentView(R.layout.activity\_main);
19.         newProblem(); //generate a new problem when the app starts
20.     }
21.  
22.     public void checkAnswer(View view) {
23.         EditText editText = findViewById(R.id.answer);
24.         int userAnswer;
25.         try {
26.             userAnswer = Integer.parseInt(editText.getText().toString());
27.         } catch (NumberFormatException e) {
28.             editText.setError("Invalid answer!");
29.             return;
30.         }
31.         if (userAnswer == answer) {
32.             score++;
33.             TextView textView = findViewById(R.id.score);
34.             textView.setText("Score: " + score);
35.             TextView message = findViewById(R.id.message);
36.             message.setText("Correct!");
37.         } else {
38.             TextView message = findViewById(R.id.message);
39.             message.setText("Sorry, the correct answer was " + answer + ".");
40.         }
41.     }
42.  
43.     public void playAgain(View view) {
44.         newProblem();
45.         score = 0;
46.         TextView textView = findViewById(R.id.score);
47.         textView.setText("Score: 0");
48.     }
49.  
50.     private void newProblem() {
51.         Random random = new Random();
52.         int operator = random.nextInt(4); //generating a number to determine the operator
53.         switch (operator) {
54.             case 0: //addition
55.                 num1 = random.nextInt(51); //generate a random number between 0 and 50
56.                 num2 = random.nextInt(51); //generate another random number between 0 and 50
57.                 answer = num1 + num2;
58.                 break;
59.             case 1: //subtraction
60.                 num1 = random.nextInt(101);
61.                 num2 = random.nextInt(num1+1); //generate a number between 0 and num1
62.                 answer = num1 - num2;
63.                 break;
64.             case 2: //multiplication
65.                 num1 = random.nextInt(13); //generate a random number between 0 and 12
66.                 num2 = random.nextInt(13);
67.                 answer = num1*num2;
68.                 break;
69.             case 3: //division
70.                 num1 = random.nextInt(13) * random.nextInt(13); //multiply two random numbers between 0 and 12 to get num1
71.                 num2 = random.nextInt(12) + 1; //generate a random number between 1 and 12 for num2
72.                 answer = num1 / num2;
73.                 break;
74.         }
75.  
76.         TextView textView = findViewById(R.id.problem);
77.         textView.setText(num1 + " ? " + num2 + " = ?");
78.         TextView message = findViewById(R.id.message);
79.         message.setText("");
80.         EditText editText = findViewById(R.id.answer);
81.         editText.setText("");
82.     }
83. }
84.