#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <ctime>
#include <iomanip>

using namespace std;

void quiz(int level, int selected_operation) {
    srand( time(NULL) );
    int a, b;
    int answer;
    int operation = selected_operation;

    while ( answer != -1 ) {
        if (selected_operation == 5)
            operation = rand() % 4 + 1;
        a = rand() % 100 + 1;
        b = rand() % 100 + 1;
        if (level == 1) {
            a /= 10;
            b /= 10;
        }
        cout << "Type your answer (-1 to quit): " << endl;
        cout << setw(4) << a << endl;
        int correct_answer;
        switch (operation) {
        case 1:
            cout << "+";
            correct_answer = a + b;
            break;
        case 2:
            cout << "-";
            correct_answer = a - b;
            break;
        case 3:
            cout << "x";
            correct_answer = a * b;
            break;
        case 4:
            cout << "/";
            correct_answer = a / b;
            break;
        }
        cout << setw(3) << b << endl;
        cout << "----" << endl;
        cin >> answer;
        while (answer != correct_answer && answer != -1) {
            cout << "Try again." << endl;
            cin >> answer;
        }
        if (answer == correct_answer)
            cout << "Correct answer!\n" << endl;
    }
    cout << endl;
}

int main()
{
    int level, operation;
    do {
        cout << "Enter your graduation level:\n1. Beginner\n2. Advanced" << endl;
        cin >> level;
        switch (level) {
        case 1:
        case 2:
            cout << "Enter the exercises you would like to take:\n1. Addition\n2. Subtraction\n3. Multiplication\n4. Division\n5. Random" << endl;
            cin >> operation;
            switch (operation) {
            case 1:
            case 2:
            case 3:
            case 4:
            case 5:
                quiz(level, operation);
                break;
            default:
                if ( cin.get() != EOF )
                    cout << "Invalid choice." << endl;
            }
            break;
        default:
            if ( cin.get() != EOF )
                cout << "Invalid choice." << endl;
        }
    } while ( cin.get() != EOF );

    return 0;
}