/// <summary>
/// calls the ConsoleView.DisplayGetNumberOfUnitsToSell method and the SubtractProduct method if a valid integer is returned
/// </summary>
private void Sell()
{
int numberOfUnits = _consoleView.DisplayGetNumberOfUnitsToSell(_salesperson.CurrentStock);
_salesperson.CurrentStock.SubtractProducts(numberOfUnits);
if (_salesperson.CurrentStock.OnBackorder)
{
_consoleView.DisplayBackOrderNotification(_salesperson.CurrentStock, numberOfUnits);
}
}