public static Customer AddCustomer(this CustomerData customerData, string firstName, string lastName, string address, string city, string state, string zipCode)
{
int customerNumber = customerData.Any() ? customerData.Max(m => m.CustomerNumber) + 1 : CustomerData.CustomerNumberSeed;
Customer customer = new Customer()
{
CustomerNumber = customerNumber, FirstName = firstName, LastName = lastName, Address = address, City = city, State = state, ZipCode = zipCode
};
customerData.Add(customer);
return(customer);
}