Update array in C++ Checkout Simulation

Currently I am working on a project to Simulate a Grocery Store with :

1 super express lane

2 express lanes

1 regular lane

The issue I have come across is trying to store my random generator for the # of items each customer holds into the array so that at the end I can add up all the values to calculate the max items that were bought in each lane.

I have the following files:

LinkedList.h

ListNode.h

Passenger.h

Queue.h

Random.h

I won't show every one of them but just the snippet of codes that matter/involve with my main code that calls the random generator.

In Random.h I have the following:

#ifndef RANDOM_H
#define RANDOM_H

#include <cstdlib>
#include <ctime>


class Random {


    public:
    Random() {

    srand((unsigned)time(0));
    }

    Random(int value) {
    srand(value);}

    //Return random integer range 0 -> 1
    double next_double() {

     return double(rand()) / RAND_MAX;
    }


    int item_purchase(int n) {

    //make a case using a number 1-100(100 is max number of items they can have)
    n = (rand() % 100) + 1;

    return int(next_double() * n);
    }

The function that generates the items purchased function in Random.h is in my Checkout_Simulation.h file. The function I am working on is:

template <typename NODETYPE>
void Checkout_Simulation<NODETYPE> :: run_sim() {

    int number = 0;
    static int const SIZE = 0;
    int super_items[SIZE] = {0};
    int ex1_items[SIZE] = {0};
    int ex2_items[SIZE] = {0};
    int regular_items[SIZE] = {0};


    for(clock_time = 0, clock_time <total_time; clock_time++){


    item_obj.item_purchase(number);



    if (number < 15) {
      super_express.check_new_arrival(clock_time, display_all);

    }
    else if (number >15 && number <=20){

      express_line1.check_new_arrival(clock_time, display_all);
      express_line2.check_new_arrival(clock_time, display_all);
    }
    else {
      regular_line.check_new_arrival(clock_time, display_all);
    }



    if (clock_time >= finish_time){
            start_checkout();
      }

    }//end for loop
}

Queue.h check_new_arrival function so you can understand that this adds a customer

//See nitial_rate = new_rate;
template <typename NODETYPE>
void Queue :: check_new_arrival(int clock, bool display_all){

int number = 0;

    if (simulation_obj.next_doubleValue < initial_rate) {

            current_queue.push(Passenger(clock_time));

      if(display_all) {
            cout <<"Time is " << clock << ": " << queue_name
                    << " arrival, new queue size is "
                    << current.queue.size() <<endl;
      }

    }
}

So what I want is for example, the random number comes out as 10. It will go to the if statement of number <15 in run_sim()... following the other if nested statements and update the array. How do I implement this? I can't exactly make a for loop to add them since it Simulates and goes through this function once at a time. Please help explain and give me some direction. I would appreciate it!