Something

//main question
//what happens next?
//-Departure
//-Arrival

//in.txt
//main.exe
//main.exe < in.txt puts the contents of in.txt into CIN

#include <iostream>
#include <queue>
using namespace std;

struct Customer
{
    int arrival_time;
    int items;
    Customer(int a, int i)
    {
        arrival_time = a;
        items = i;
    }
    Customer()
    {
              arrival_time = 0;
              items = 0;
    }
};

class Checkout
{
    public:
        void depart();
        void arrive(Customer c);
        bool empty() const;
        int next_departure_time() const;
    private:
        queue<Customer> q_;
        int departure_time_;
};

void Checkout::arrive(Customer c)
{
    q_.push(c);
    if(empty())
    {
        departure_time_ = c.arrival_time + c.items;
        //print out arrival event
    }
}
void Checkout::depart()
{
    //assert queue isn't empty assert(!empty())
    Customer c = q_.front();
    q_.pop();
    if(!q_.empty())
    departure_time_ += q_.front().items;
    //departure event
}
bool Checkout::empty() const
{
    return q_.empty();
}
int Checkout::next_departure_time() const
{
    //assert(!empty());
    return departure_time_;
}

int main()
{   
    Checkout checkout;
    int arrival = 0;
    int items = 0;
    while(cin >> arrival >> items)
    Customer customer(arrival, items);
        while(!checkout.empty() && checkout.next_departure_time() <= arrival)
        //only makes sense as long as queue isn't empty
        {
               checkout.depart();
        }

        while(!checkout.empty())
        {
            checkout.arrive(customer));
        }


        while(!checkout.empty())
        {
            checkout.depart();
        }
}