VendingMachineProgram

using System;

namespace VendingMachine
{
    class Program
    {
        static void Main(string[] args)
        {
            // 1. read input
            string input = Console.ReadLine();
            double balance = 0;
            double[] validCoins = {0.1, 0.2, 0.5, 1, 2};

            // 2. while not start, sum coins
            while (input != "Start")
            {
                double coin = double.Parse(input);
                bool isValidCoin = false;

                // 2.1 only accept 0.1, 0.2, 0.5, 1, 2
                for (int i = 0; i < validCoins.Length; i++)
                {
                    // 3. sum the money
                    if (coin == validCoins[i])
                    {
                        isValidCoin = true;
                        balance += coin;
                    }
                }

                if(!isValidCoin)
                    Console.WriteLine($"Cannot accept {coin}");

                input = Console.ReadLine();
            }

            // 4. while not end, buy products
            input = Console.ReadLine();
            double[] productsPrice = {2,    0.7,   1.5,   0.8,  1.0 };
            //Products =            {Nuts, Water, Crisps, Soda, Coke}
            string[] products = { "Nuts", "Water", "Crisps", "Soda", "Coke" };

            while (input != "End")
            {
                bool isPurchased = false;
                bool isValidProduct = false;

                for (int i = 0; i < products.Length; i++)
                {
                    if (input == products[i])
                    {
                        isValidProduct = true;
                        // 4.1 balance -= productPrice
                        if (balance >= productsPrice[i])
                        {
                            balance -= productsPrice[i];
                            Console.WriteLine($"Purchased {products[i]}");
                            isPurchased = true;
                        }
                    }
                }

                if(!isValidProduct)
                    Console.WriteLine("Invalid product");

                if (!isPurchased && isValidProduct)
                    Console.WriteLine("Sorry, not enough money");

                input = Console.ReadLine();
            }

            // 5. Print(Change: {money left})
            Console.WriteLine($"Change: {balance:f2}");
        }
    }
}