Introduction

From now on, we will try to always indicate the type of exception that could be thrown if something goes wrong in a program

When studying data formatting in Lesson 5, we saw that everything the user types into an application using the keyboard is primarily a string and that you must convert it to the appropriate type before using it. When you request a specific type of value from the user, after the user has typed it and you decide to convert it to the appropriate type, if your conversion fails, the program produces an error. The error is of the FormatException class.

Here is a program that deals with a FormatException exception:

using System;

class Program
{
    static int Main()
    {
        double side;

        Console.WriteLine("Square Processing");
        try
        {
            Console.Write("Enter Side: ");
            side = double.Parse(Console.ReadLine());

            Console.WriteLine("\nSquare Characteristics");
            Console.WriteLine("Side:      {0}", side);
            Console.WriteLine("Perimeter: {0}", side * 4);
        }
        catch(FormatException)
        {
            Console.WriteLine("\nYou typed an invalid number");
        }

        return 0;
    }
}

Here is an example of running the program:

Square Processing
Enter Side: 25.9G

You typed an invalid number
Press any key to continue . . .

1. Change the OrderProcessing.cs file as follows (this includes the complete current version of the file):
    

   using System; namespace GeorgetownCleaningServices4 { class OrderProcessing { #region Objects used to process an order // Price of items const decimal PriceOneShirt = 0.95M; const decimal PriceAPairOfPants = 2.95M; const decimal PriceOneDress = 4.55M; const decimal TaxRate = 0.0575M; // 5.75% CleaningOrderInfo cleaningOrder; // Each of these sub totals will be used for cleaning items private decimal SubTotalShirts; private decimal SubTotalPants; private decimal SubTotalDresses; // Values used to process an order private decimal TotalOrder; private decimal TaxAmount; private decimal SalesTotal; private decimal AmountTended; private decimal Difference; #endregion #region Actions used to process and present an order public OrderProcessing() { cleaningOrder = new CleaningOrderInfo(); } public void ProcessOrder() { Console.WriteLine("-/- Georgetown Cleaning Services -/-"); // Request order information from the user Console.Write("Enter Customer Name: "); cleaningOrder.CustomerName = Console.ReadLine(); Console.Write("Enter Customer Phone: "); cleaningOrder.HomePhone = Console.ReadLine(); try { Console.Write("Enter the order date(mm/dd/yyyy): "); cleaningOrder.OrderDate = DateTime.Parse(Console.ReadLine()); } catch (FormatException) { Console.WriteLine("The value you entered is not a valid date"); } try { Console.Write("Enter the order time(hh:mm AM/PM): "); cleaningOrder.OrderTime = DateTime.Parse(Console.ReadLine()); } catch { Console.WriteLine("The value you entered is not a valid time"); } // Request the quantity of each category of items try { Console.Write("Number of Shirts: "); cleaningOrder.NumberOfShirts = uint.Parse(Console.ReadLine()); if (cleaningOrder.NumberOfShirts < uint.MinValue) throw new OverflowException("Negative value not " + "allowed for shirts"); } catch (FormatException) { Console.WriteLine("The value you typed for the number of " + "shirts is not a valid number"); } try { Console.Write("Number of Pants: "); cleaningOrder.NumberOfPants = uint.Parse(Console.ReadLine()); } catch(FormatException) { Console.WriteLine("The value you typed for the number of " + "pair or pants is not a valid number"); } try { Console.Write("Number of Dresses: "); cleaningOrder.NumberOfDresses = uint.Parse(Console.ReadLine()); } catch(FormatException) { Console.WriteLine("The value you typed for the number of " + "dresses is not a valid number"); } // Perform the necessary calculations SubTotalShirts = cleaningOrder.NumberOfShirts * PriceOneShirt; SubTotalPants = cleaningOrder.NumberOfPants * PriceAPairOfPants; SubTotalDresses = cleaningOrder.NumberOfDresses * PriceOneDress; // Calculate the "temporary" total of the order TotalOrder = SubTotalShirts + SubTotalPants + SubTotalDresses; // Calculate the tax amount using a constant rate TaxAmount = TotalOrder * TaxRate; // Add the tax amount to the total order SalesTotal = TotalOrder + TaxAmount; // Communicate the total to the user... Console.WriteLine("\nThe Total order is: {0:C}", SalesTotal); // and request money for the order try { Console.Write("Amount Tended? "); AmountTended = decimal.Parse(Console.ReadLine()); } catch(FormatException) { Console.WriteLine("You were asked to enter an " + "amount of money but..."); } // Calculate the difference owed to the customer // or that the customer still owes to the store Difference = AmountTended - SalesTotal; ShowReceipt(); } private void ShowReceipt() { Console.WriteLine(); // Display the receipt Console.WriteLine("===================================="); Console.WriteLine("-/- Georgetown Cleaning Services -/-"); Console.WriteLine("===================================="); Console.WriteLine("Customer: {0}", cleaningOrder.CustomerName); Console.WriteLine("Home Phone: {0}", cleaningOrder.HomePhone); Console.WriteLine("Order Date: {0:D}", cleaningOrder.OrderDate); Console.WriteLine("Order Time: {0:t}", cleaningOrder.OrderTime); Console.WriteLine("------------------------------------"); Console.WriteLine("Item Type Qty Unit/Price Sub-Total"); Console.WriteLine("------------------------------------"); Console.WriteLine("Shirts {0,3} {1,4} {2,6}", cleaningOrder.NumberOfShirts, PriceOneShirt, SubTotalShirts); Console.WriteLine("Pants {0,3} {1,4} {2,6}", cleaningOrder.NumberOfPants, PriceAPairOfPants, SubTotalPants); Console.WriteLine("Dresses {0,3} {1,4} {2,6}", cleaningOrder.NumberOfDresses, PriceOneDress, SubTotalDresses); Console.WriteLine("------------------------------------"); Console.WriteLine("Total Order: {0,6}", TotalOrder.ToString("C")); Console.WriteLine("Tax Rate: {0,6}", TaxRate.ToString("P")); Console.WriteLine("Tax Amount: {0,6}", TaxAmount.ToString("C")); Console.WriteLine("Net Price: {0,6}", SalesTotal.ToString("C")); Console.WriteLine("------------------------------------"); Console.WriteLine("Amount Tended: {0,6}", AmountTended.ToString("C")); Console.WriteLine("Difference: {0,6}", Difference.ToString("C")); Console.WriteLine("===================================="); } #endregion } }

2. Execute the application and test it. Here is an example:
    

   -/- Georgetown Cleaning Services -/- Enter Customer Name: Allen Dons Enter Customer Phone: 202-442-0400 Enter the order date(mm/dd/yyyy): 7/14/2005 Enter the order time(hh:mm AM/PM): 8:46 AM Number of Shirts: 5 Number of Pants: 2 Number of Dresses: 0 The Total order is: $11.26 Amount Tended? 15 ==================================== -/- Georgetown Cleaning Services -/- ==================================== Customer: Allen Dons Home Phone: 202-442-0400 Order Date: Thursday, July 14, 2005 Order Time: 8:46 AM ------------------------------------ Item Type Qty Unit/Price Sub-Total ------------------------------------ Shirts 5 0.95 4.75 Pants 2 2.95 5.90 Dresses 0 4.55 0.00 ------------------------------------ Total Order: $10.65 Tax Rate: 5.75 % Tax Amount: $0.61 Net Price: $11.26 ------------------------------------ Amount Tended: $15.00 Difference: $3.74 ==================================== Press any key to continue . . .

3. Close the DOS window

A computer application receives, processes, and produces values on a regular basis as the program is running. To better manage these values, as we saw when studying variables and data types in Lesson 1 and Lesson 2, the compiler uses appropriate amounts of space to store its values. It is not unusual that either you the programmer or a user of your application provides an value that is beyond the allowed range based on the data type. For example, we saw that a byte uses 8 bits to store a value and a combination of 8 bits can store a number no more than 255. If you provide a value higher than 255 to be stored in a byte, you get an error. Consider the following program:

using System;

// An Exercise class
class Exercise
{ 
    static int Main()
    {
	byte NumberOfPages;

	Console.Write("Enter the number of pages of the newspaper: ");
	NumberOfPages = byte.Parse(Console.ReadLine());

	Console.WriteLine("Number of Pages of the Newspaper: {0}\n", NumberOfPages);
    }

    return 0;
}

When a value beyond the allowable range is asked to be stored in memory, the compiler produces (the expression is "throws" as we will learn soon) an error of the OverflowException class. Here is an example of running the program:

Enter the number of pages of the newspaper: 824

Unhandled Exception: System.OverflowException: Value was either too large or too
 small for an unsigned byte.
   at System.Byte.Parse(String s, NumberStyles style, IFormatProvider provider)
   at System.Byte.Parse(String s)
   at Exercise.Main() in c:\programs\msvcs .net 2003\project17\exercise.cs:line
11

As with the other errors, when this exception is thrown, you should take an appropriate action.

Once again, when studying the techniques of converting or formatting values in Lesson 5, we saw that a value was passed to the Parse() method of its data type for analysis. For a primitive data type, the Parse() method scans the string and if the string cannot be converted into a valid value, the compiler usually produces a FormatException exception as we saw above. Other classes such as DateTime also use a Parse() method to scan the value submitted to it. For example, if you request a date value from the user, the DateTime.Parse() method scans the string to validate it. In US English, Parse() expects the user to type a string in the form m/d/yy or mm/dd/yy or mm/dd/yyyy. Consider the following program:

using System;

// An Exercise class
class Exercise
{ 
    static int Main()
    {
	DateTime DateHired;

	Console.Write("Enter Date Hired: ");
	DateHired = DateTime.Parse(Console.ReadLine());

	Console.WriteLine("Date Hired: {0:d}\n", DateHired);

	return 0;
    }
}

If the user types a value that cannot be converted into a valid date, the compiler produces an ArgumentOutOfRangeException exception. Here is an example of running the above program: