Очередь

using System;
using System.Collections.Generic;

namespace store
{
    class Program
    {
        static void Main(string[] args)
        {
            Random random = new Random();
            Queue<int> customers = new Queue<int>();
            int queueSize = 5;
            int maxPurchaseAmount = 1000;
            int storeBalance = 0;

            for (int i = 0; i < queueSize; i++)
                customers.Enqueue(random.Next(maxPurchaseAmount));

            while (customers.Count != 0)
            {
                Console.Clear();
                int amount = ServiceCustomer(customers);
                TopUpBalance(amount, ref storeBalance);
                Console.WriteLine($"Длина очереди: {customers.Count}");
                Console.ReadKey();
            }
        }

        private static int ServiceCustomer(Queue<int> queue)
        {
            int purchaseAmount = queue.Dequeue();
            Console.WriteLine($"Покупатель купил товаров на {purchaseAmount} рублей");
            return purchaseAmount;
        }

        private static void TopUpBalance(int amount, ref int storeBalance)
        {
            storeBalance += amount;
            Console.WriteLine($"На балансе магазина {storeBalance} рублей");
        }
    }
}