silly question/answer quiz example (C++11)

quiz.cpp

#include <string>
#include <vector>
#include <iostream>
#include <fstream>
#include <sstream>
#include <algorithm>
#include <cassert>
using namespace std;

class Quiz {

    vector<pair<string, string>> questions;
    vector<string> answers;

  public:

    Quiz(const string& filename) {
        ifstream f { filename };
        string answer, question;
        while(getline(f, answer) && getline(f, question)) {
            questions.emplace_back(question, answer);
            answers.emplace_back(answer);
        }
    }

    size_t num_questions() const { return questions.size(); }

    bool ask(size_t question_num, size_t num_answers = 3) {
        
        // get and print the question
        assert(question_num < questions.size());
        const string& ques = questions[question_num].first;
        const string& correct_ans = questions[question_num].second;
        cout << "Question: " << ques << "\n";

        // build a vector containing the correct answer and (num_answers - 1) randomly chosen incorrect answers
        partition(begin(answers), end(answers), [&] (const string& ans) { return ans == correct_ans; });
        random_shuffle(begin(answers) + 1, end(answers));
        vector<string> possible_answers(begin(answers), begin(answers) + min(answers.size(), num_answers));
        
        // display the choices in random order
        random_shuffle(begin(possible_answers), end(possible_answers));
        for(size_t i = 0; i < possible_answers.size(); ++i)
            cout << i + 1 << ". " << possible_answers[i] << "\n";

        // take input until a valid response is seen
        for(string response; cout << "Answer: " && getline(cin, response); cout << "Bad input, try again.\n") {
            istringstream ss(response);
            size_t i;
            if(ss >> i && i >= 1 && i <= possible_answers.size()) {
                if(possible_answers[i - 1] == correct_ans) {
                    cout << "Correct\n\n";
                    return true;
                } else {
                    cout << "Wrong\n\n";
                    return false;
                }
            }
        }
        return false;
    }
};

int main(int argc, char **argv)
{
    assert(argc == 2);
    
    Quiz q { argv[1] };
    size_t correct = 0;
    for(size_t i = 0; i < q.num_questions(); ++i)
        correct += q.ask(i);
    cout << "\n\nYou got " << correct << " out of " << q.num_questions() << "\n";
}