|
More than any other assignment, file processing is in prime
need of exception handling. As we will see in the next section, during file
processing, there are many things that can go wrong. For this reason, the
creation and/or management of streams should be performed in a try block
to get ready to handle exceptions that would occur. Besides actually handling
exceptions, the C# language provides a special keyword used free resources. This
keyword is finally.
The finally keyword is used to create a section of an
exception. Like catch, a finally block cannot exist by itself. It can be created
following a try section. The formula used would be:
try
{
}
finally
{
}
Based on this, the finally section has a body of its
own, delimited by its curly brackets. Like catch, the finally section is
created after the try section. Unlike catch, finally never
has parentheses and never takes arguments. Unlike catch, the finally
section is always executed. Because the finally clause always gets
executed, you can include any type of code in it but it is usually appropriate
to free the resources that were allocated earlier. Here is an example:
using System;
using System.IO;
public class Program
{
static int Main(string[] args)
{
var Filename = "Members.clb";
var fstPersons = new FileStream(Filename, FileMode.Create);
var wrtPersons = new BinaryWriter(fstPersons);
try
{
wrtPersons.Write("James Bloch");
wrtPersons.Write("Catherina Wallace");
wrtPersons.Write("Bruce Lamont");
wrtPersons.Write("Douglas Truth");
}
finally
{
wrtPersons.Close();
fstPersons.Close();
}
return 0;
}
}
In the same way, you can use a finally section to free
resources used when reading from a stream:
using System;
using System.IO;
public class Program
{
static int Main(string[] args)
{
/* var Filename = "Members.clb";
var fstPersons = new FileStream(Filename, FileMode.Create);
var wrtPersons = new BinaryWriter(fstPersons);
try
{
wrtPersons.Write("James Bloch");
wrtPersons.Write("Catherina Wallace");
wrtPersons.Write("Bruce Lamont");
wrtPersons.Write("Douglas Truth");
}
finally
{
wrtPersons.Close();
fstPersons.Close();
}*/
var strLine = "";
var Filename = "Members.clb";
var fstMembers = new FileStream(Filename, FileMode.Open);
var rdrMembers = new BinaryReader(fstMembers);
try
{
strLine = rdrMembers.ReadString();
Console.WriteLine(strLine);
strLine = rdrMembers.ReadString();
Console.WriteLine(strLine);
strLine = rdrMembers.ReadString();
Console.WriteLine(strLine);
strLine = rdrMembers.ReadString();
Console.WriteLine(strLine);
}
finally
{
rdrMembers.Close();
fstMembers.Close();
}
return 0;
}
}
Of course, since the whole block of code starts with a
try section, it is used for exception handling. This means that you can add
the necessary and appropriate catch section(s) but you don't have to.
|
 Practical
Learning: Finally Releasing Resources
|
|
- Start Microsoft Visual C# and create a Console Application named
IceCream4
- To save the project, on the Standard toolbar, click the Save All button
- Change the Solution Name to VendingMachine4
- Accept the Name of the project as IceCream3 and click Save
- To create a new class, on the main menu, click Project -> Add Class...
- Set the Name to IceCream and click Add
- Change the file as follows:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
namespace IceCream4
{
delegate void Request();
// This class is used to create and manage an Ice Cream
// and to process an order
public sealed class IceCream
{
// This is the base price of an Ice Cream
// Optional values may be added to it
public const decimal BasePrice = 1.55M;
// These arrays are used to build the components
// of various ice creams
private string[] Flavor;
private string[] Container;
private string[] Ingredient;
// Additional factor used to process an Ice Cream order
private int Scoops;
private decimal TotalPrice;
// Variables that will hold the user's choice
// These are declared "globally" so they can be
// shared among methods
int ChoiceFlavor;
int ChoiceContainer;
int ChoiceIngredient;
// This default constructor is the best place for
// us to initialize the array
public IceCream()
{
Flavor = new string[10];
Flavor[0] = "Vanilla";
Flavor[1] = "Cream of Cocoa";
Flavor[2] = "Chocolate Chip";
Flavor[3] = "Organic Strawberry";
Flavor[4] = "Butter Pecan";
Flavor[5] = "Cherry Coke";
Flavor[6] = "Chocolate Brownies";
Flavor[7] = "Caramel Au Lait";
Flavor[8] = "Chunky Butter";
Flavor[9] = "Chocolate Cookie";
Ingredient = new string[4];
Ingredient[0] = "No Ingredient";
Ingredient[1] = "Peanuts";
Ingredient[2] = "M & M";
Ingredient[3] = "Cookies";
Container = new string[3];
Container[0] = "Cone";
Container[1] = "Cup";
Container[2] = "Bowl";
}
// This method requests a flavor from the user and
// returns the choice
internal void ChooseFlavor()
{
// Make sure the user selects a valid number
//that represents a flavor...
do
{
// In case the user types a symbol that
// is not a number
try
{
Console.WriteLine("What type of flavor do you want?");
for (int i = 0; i < Flavor.Length; i++)
Console.WriteLine("{0} - {1}", i + 1, Flavor[i]);
Console.Write("Your Choice? ");
ChoiceFlavor = int.Parse(Console.ReadLine());
}
catch (FormatException) // display an appropriate message
{
Console.WriteLine("You must enter a valid number " +
"and no other character!");
}
// If the user typed an invalid number out of the
// allowed range
// let him or her know and provide another chance
if (ChoiceFlavor < 1 || ChoiceFlavor > Flavor.Length)
Console.WriteLine("Invalid Choice - Try Again!\n");
} while (ChoiceFlavor < 1 || ChoiceFlavor > Flavor.Length);
}
// This method allows the user to select a container
internal void ChooseContainer()
{
// Make sure the user selects a valid number that
// represents a container
do
{
// If the user types a symbol that is not a number
try
{
Console.WriteLine("What type of container do you want?");
for (int i = 0; i < Container.Length; i++)
Console.WriteLine("{0} - {1}", i + 1, Container[i]);
Console.Write("Your Choice? ");
ChoiceContainer = int.Parse(Console.ReadLine());
}
catch (FormatException) // display an appropriate message
{
Console.WriteLine("You must enter a valid " +
"number and no other character!");
}
// If the user typed an invalid number out of the
// allowed range
// let him or her know and provide another chance
if ((ChoiceContainer < 1) ||
(ChoiceContainer > Container.Length))
Console.WriteLine("Invalid Choice - Try Again!");
} while ((ChoiceContainer < 1) ||
(ChoiceContainer > Container.Length));
}
internal void ChooseIngredient()
{
do
{
try
{
Console.WriteLine("Do you want an ingredient or not");
for (int i = 0; i < Ingredient.Length; i++)
Console.WriteLine("{0} - {1}",
i + 1,
Ingredient[i]);
Console.Write("Your Choice? ");
ChoiceIngredient = int.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("You must enter a valid " +
"number and no other character!");
}
if ((ChoiceIngredient < 1) ||
(ChoiceIngredient > Ingredient.Length))
Console.WriteLine("Invalid Choice - Try Again!");
} while ((ChoiceIngredient < 1) ||
(ChoiceIngredient > Ingredient.Length));
}
internal void SpecifyNumberOfScoops()
{
do
{
try
{
Console.Write("How many scoops(1, 2, or 3)? ");
Scoops = int.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("You must enter a valid number " +
"and no other character!");
}
if (Scoops < 1 || Scoops > 3)
Console.WriteLine("Invalid Choice - Try Again!");
} while (Scoops < 1 || Scoops > 3);
}
// This method is used to process a customer order
// It uses the values of the above methods
internal void ProcessAnOrder()
{
// int ChoiceFlavor;
// int ChoiceContainer;
// int ChoiceIngredient;
decimal PriceIngredient, PriceScoop;
// Let the user know that this is a vending machine
Console.WriteLine("=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=");
Console.WriteLine("Ice Cream Vending Machine");
Console.WriteLine("-----------------------------------");
// Let the user select the components of the Ice Cream
Request Get = new Request(ChooseFlavor);
Get();
Console.WriteLine("-----------------------------------");
Get = new Request(ChooseContainer);
Get();
Console.WriteLine("-----------------------------------");
Get = new Request(ChooseIngredient);
Get();
Console.WriteLine("-----------------------------------");
Get = new Request(SpecifyNumberOfScoops);
Get();
Console.WriteLine("-----------------------------------");
// If the user selects an ingredient instead of "No Ingredient",
// add $0.50 to the order
if ((ChoiceIngredient == 2) ||
(ChoiceIngredient == 3) ||
(ChoiceIngredient == 4))
PriceIngredient = 0.50M;
else
PriceIngredient = 0.00M;
// Instead of multiplying a number scoops to a value,
// We will use an incremental value depending on
// the number of scoops
if (Scoops == 1)
PriceScoop = 0.65M;
else if (Scoops == 2)
PriceScoop = 1.05M;
else
PriceScoop = 1.55M;
// Calculate the total price of the Ice Cream
TotalPrice = BasePrice + PriceScoop + PriceIngredient;
// Create the Ice Cream...
// And display a receipt to the user
DisplayReceipt();
}
// This method is used to display a receipt to the user
internal void DisplayReceipt()
{
Console.WriteLine("\n=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=");
Console.WriteLine("Ice Cream Order");
Console.WriteLine("-----------------------------------");
Console.WriteLine("Flavor: {0}",
Flavor[ChoiceFlavor - 1]);
Console.WriteLine("Container: {0}",
Container[ChoiceContainer - 1]);
Console.WriteLine("Ingredient: {0}",
Ingredient[ChoiceIngredient - 1]);
Console.WriteLine("Scoops: {0}", Scoops);
Console.WriteLine("Total Price: {0:C}", TotalPrice);
Console.WriteLine("=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=\n");
}
internal void SaveOrder()
{
string strFilename;
Console.Write("Please enter your initials or the name " +
"we will use to remember your order: ");
strFilename = Console.ReadLine();
strFilename = strFilename + ".icr";
// Find out if the user entered a name of a file
// that is already in the machine
if (File.Exists(strFilename))
{
char answer;
FileStream stmIceCream =
new FileStream(strFilename, FileMode.Create);
BinaryWriter bnwIceCream =
new BinaryWriter(stmIceCream);
try
{
// If so, find out if the user wants to
// replace the old file
Console.WriteLine("The file you entered exists already.");
Console.Write("Do you want to replace it(y/n)?");
answer = char.Parse(Console.ReadLine());
// If the customer wants to replace it...
if (answer == 'y' || answer == 'Y')
{
// ... do so
Console.WriteLine("The former order with the same " +
"name will be replaced");
Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
Console.WriteLine(" Saving Order: {0}", strFilename);
bnwIceCream.Write(Flavor[ChoiceFlavor - 1]);
bnwIceCream.Write(Container[ChoiceContainer - 1]);
bnwIceCream.Write(Ingredient[ChoiceIngredient - 1]);
bnwIceCream.Write(Scoops);
bnwIceCream.Write(TotalPrice);
}
// If the customer wants to save the new order with
// a different name
else if (answer == 'n' || answer == 'N')
{
// Ask the user to enter a name to remember the order
Console.Write("Please enter a name we will use " +
"to remember this order: ");
strFilename = Console.ReadLine();
strFilename = strFilename + ".icr";
stmIceCream =
new FileStream(strFilename, FileMode.Create);
bnwIceCream = new BinaryWriter(stmIceCream);
Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
Console.WriteLine(" Saving Order: {0}", strFilename);
bnwIceCream.Write(Flavor[ChoiceFlavor - 1]);
bnwIceCream.Write(Container[ChoiceContainer - 1]);
bnwIceCream.Write(Ingredient[ChoiceIngredient - 1]);
bnwIceCream.Write(Scoops);
bnwIceCream.Write(TotalPrice);
}
else
Console.WriteLine("Invalid Answer - We will close");
}
finally
{
bnwIceCream.Close();
stmIceCream.Close();
}
}
else
{
FileStream stmIceCream =
new FileStream(strFilename, FileMode.Create);
BinaryWriter bnwIceCream =
new BinaryWriter(stmIceCream);
try
{
Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
Console.WriteLine(" Saving Order: {0}", strFilename);
bnwIceCream.Write(Flavor[ChoiceFlavor - 1]);
bnwIceCream.Write(Container[ChoiceContainer - 1]);
bnwIceCream.Write(Ingredient[ChoiceIngredient - 1]);
bnwIceCream.Write(Scoops);
bnwIceCream.Write(TotalPrice);
}
finally
{
bnwIceCream.Close();
stmIceCream.Close();
}
}
}
internal void OpenOrder()
{
string strFilename;
string SelectedFlavor;
string SelectedContainer;
string SelectedIngredient;
// Ask the user to enter a name of a previously saved order
Console.Write("Please enter the name you previously " +
"gave to remember your order: ");
strFilename = Console.ReadLine();
strFilename = strFilename + ".icr";
FileStream stmIceCream =
new FileStream(strFilename, FileMode.Open);
BinaryReader bnrIceCream =
new BinaryReader(stmIceCream);
try
{
// Find out if this order was previously saved in the machine
if (File.Exists(strFilename))
{
// If so, open it
SelectedFlavor = bnrIceCream.ReadString();
SelectedContainer = bnrIceCream.ReadString();
SelectedIngredient = bnrIceCream.ReadString();
Scoops = bnrIceCream.ReadInt32();
TotalPrice = bnrIceCream.ReadDecimal();
// And display it to the user
Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
Console.WriteLine(" Previous Order: {0}", strFilename);
Console.WriteLine("Flavor: {0}", SelectedFlavor);
Console.WriteLine("Container: {0}", SelectedContainer);
Console.WriteLine("Ingredient: {0}", SelectedIngredient);
Console.WriteLine("Scoops: {0}", Scoops);
Console.WriteLine("Total Price: {0:C}\n", TotalPrice);
}
else
Console.WriteLine("The name you entered is not " +
"registered in our previous orders");
}
finally
{
bnrIceCream.Close();
stmIceCream.Close();
}
}
}
}
Access the Program.cs file and change it as follows:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace IceCream4
{
public class Program
{
static void Main(string[] args)
{
var answer = 'n';
var ic = new IceCream();
var process = new Request(ic.ProcessAnOrder);
Console.Write("Do you want to re-order a previously " +
"saved order(y/n)? ");
answer = char.Parse(Console.ReadLine());
if (answer == 'y' || answer == 'Y')
ic.OpenOrder();
else
{
process();
Console.Write("Do you want us to remember this " +
"order the next time you come to " +
"get your Ice Cream (y/n)? ");
answer = char.Parse(Console.ReadLine());
if (answer == 'y' || answer == 'Y')
ic.SaveOrder();
else
Console.WriteLine("\nIt was nice serving you." +
"\nCome Again!!!\n");
}
}
}
}
- Execute the application and test it. Here is an example:
Do you want to re-order a previously saved order(y/n)? n
=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
Ice Cream Vending Machine
-----------------------------------
What type of flavor do you want?
1 - Vanilla
2 - Cream of Cocoa
3 - Chocolate Chip
4 - Organic Strawberry
5 - Butter Pecan
6 - Cherry Coke
7 - Chocolate Brownies
8 - Caramel Au Lait
9 - Chunky Butter
10 - Chocolate Cookie
Your Choice? 6
-----------------------------------
What type of container do you want?
1 - Cone
2 - Cup
3 - Bowl
Your Choice? 2
-----------------------------------
Do you want an ingredient or not
1 - No Ingredient
2 - Peanuts
3 - M & M
4 - Cookies
Your Choice? 1
-----------------------------------
How many scoops(1, 2, or 3)? 2
-----------------------------------
=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
Ice Cream Order
-----------------------------------
Flavor: Cherry Coke
Container: Cup
Ingredient: No Ingredient
Scoops: 2
Total Price: $2.60
=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
Do you want us to remember this order the next time you
come to get your Ice Cream (y/n)? n
It was nice serving you.
Come Again!!!
Press any key to continue . . .
- Close the DOS window
- Execute the application and test it. Indicate that you want to open an
existing file
- Enter a wrong file name such as Q4 and press Enter
Click Don't Send. Here is an
example:
Do you want to re-order a previously saved order(y/n)? y
Please enter the name you previously gave to remember your order: Q4
Unhandled Exception: System.IO.FileNotFoundException: Could not find file 'C:\Do
cuments and Settings\Administrator\My Documents\Visual Studio 2008\Projects\Vend
ingMachine4\IceCream4\bin\Release\Q4.icr'.
File name: 'C:\Documents and Settings\Administrator\My Documents\Visual Studio 2
008\Projects\VendingMachine4\IceCream4\bin\Release\Q4.icr'
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, I
nt32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions o
ptions, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy)
at System.IO.FileStream..ctor(String path, FileMode mode)
at IceCream4.IceCream.OpenOrder() in C:\Documents and Settings\Administrator\
My Documents\Visual Studio 2008\Projects\VendingMachine4\IceCream4\IceCream.cs:l
ine 362
at IceCream4.Program.Main(String[] args) in C:\Documents and Settings\Adminis
trator\My Documents\Visual Studio 2008\Projects\VendingMachine4\IceCream4\Progra
m.cs:line 21
Press any key to continue . . .
- Close the DOS window
|
.NET Framework Exception Handling for File
Processing
|
|
In the previous lesson as our introduction to file
processing, we behaved as if everything was alright. Unfortunately, file
processing can be very strict in its assignments. Based on this, the .NET
Framework provides various Exception-oriented classes to deal with almost any
type of exception you can think of.
One of the most important aspects of file processing is the
name of the file that will be dealt with. In some cases you can provide this
name to the application or document. In some other cases, you would let the user
specify the name of the path. Regardless of how the name of the file would be
provided to the operating system, when this name is acted upon, the compiler is
asked to work on the file. If the file doesn't exist, the operation cannot be
carried. Furthermore, the compiler would throw an error. There are many other
exceptions that can be thrown as a result of something going bad during file
processing:
FileNotFoundException: The exception thrown when a
file has not been found is of type FileNotFoundException. Here is an
example of handling it:
using System;
using System.IO;
public class Program
{
static int Main(string[] args)
{
/* var Filename = "Members.clb";
var fstPersons =
new FileStream(Filename, FileMode.Create);
var wrtPersons = new BinaryWriter(fstPersons);
try
{
wrtPersons.Write("James Bloch");
wrtPersons.Write("Catherina Wallace");
wrtPersons.Write("Bruce Lamont");
wrtPersons.Write("Douglas Truth");
}
finally
{
wrtPersons.Close();
fstPersons.Close();
}*/
var strLine = "";
var Filename = "Members.clc";
try
{
var fstMembers =
new FileStream(Filename, FileMode.Open);
var rdrMembers = new BinaryReader(fstMembers);
try
{
strLine = rdrMembers.ReadString();
Console.WriteLine(strLine);
strLine = rdrMembers.ReadString();
Console.WriteLine(strLine);
strLine = rdrMembers.ReadString();
Console.WriteLine(strLine);
strLine = rdrMembers.ReadString();
Console.WriteLine(strLine);
}
finally
{
rdrMembers.Close();
fstMembers.Close();
}
}
catch (FileNotFoundException ex)
{
Console.Write("Error: " + ex.Message);
Console.WriteLine(" May be the file doesn't exist " +
"or you typed it wrong!");
}
return 0;
}
}
Here is an example of what this would produce:
Error: Could not find file 'C:\Documents and Settings\Administrator\Local
Settings\Application Data\Temporary
Projects\ConsoleApplication1\bin\Release\Members.clc'.
May be the file doesn't exist or you typed it wrong!
Press any key to continue . . .
IOException: As mentioned already, during file
processing, anything could go wrong. If you don't know what caused an error, you
can throw the IOException exception.
|
Practical
Learning: Handling File Processing Exceptions
|
|
- To throw exceptions, change the file processing methods from the
IceCream.cs file as follows:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
namespace IceCream4
{
delegate void Request();
// This class is used to create and manage an Ice Cream
// and to process an order
public sealed class IceCream
{
// This is the base price of an Ice Cream
// Optional values may be added to it
public const decimal BasePrice = 1.55M;
// These arrays are used to build the components
// of various Ice Creams
// In C#, we can allocate an array's memory in
// the body of the class
private string[] Flavor;
private string[] Container;
private string[] Ingredient;
// Additional factor used to process an Ice Cream order
private int Scoops;
private decimal TotalPrice;
// Variables that will hold the user's choice
// These are declared "globally" so they can be
// shared among methods
int ChoiceFlavor;
int ChoiceContainer;
int ChoiceIngredient;
// This default constructor is the best place for
// us to initialize the array
public IceCream()
{
Flavor = new string[10];
Flavor[0] = "Vanilla";
Flavor[1] = "Cream of Cocoa";
Flavor[2] = "Chocolate Chip";
Flavor[3] = "Organic Strawberry";
Flavor[4] = "Butter Pecan";
Flavor[5] = "Cherry Coke";
Flavor[6] = "Chocolate Brownies";
Flavor[7] = "Caramel Au Lait";
Flavor[8] = "Chunky Butter";
Flavor[9] = "Chocolate Cookie";
Ingredient = new string[4];
Ingredient[0] = "No Ingredient";
Ingredient[1] = "Peanuts";
Ingredient[2] = "M & M";
Ingredient[3] = "Cookies";
Container = new string[3];
Container[0] = "Cone";
Container[1] = "Cup";
Container[2] = "Bowl";
}
// This method requests a flavor from the user and
// returns the choice
internal void ChooseFlavor()
{
// Make sure the user selects a valid number
//that represents a flavor...
do
{
// In case the user types a symbol that
// is not a number
try
{
Console.WriteLine("What type of flavor do you want?");
for (int i = 0; i < Flavor.Length; i++)
Console.WriteLine("{0} - {1}", i + 1, Flavor[i]);
Console.Write("Your Choice? ");
ChoiceFlavor = int.Parse(Console.ReadLine());
}
catch (FormatException) // display an appropriate message
{
Console.WriteLine("You must enter a valid number " +
"and no other character!");
}
// If the user typed an invalid number out of the
// allowed range
// let him or her know and provide another chance
if (ChoiceFlavor < 1 || ChoiceFlavor > Flavor.Length)
Console.WriteLine("Invalid Choice - Try Again!\n");
} while (ChoiceFlavor < 1 || ChoiceFlavor > Flavor.Length);
}
// This method allows the user to select a container
internal void ChooseContainer()
{
// Make sure the user selects a valid number that
// represents a container
do
{
// If the user types a symbol that is not a number
try
{
Console.WriteLine("What type of container do you want?");
for (int i = 0; i < Container.Length; i++)
Console.WriteLine("{0} - {1}", i + 1, Container[i]);
Console.Write("Your Choice? ");
ChoiceContainer = int.Parse(Console.ReadLine());
}
catch (FormatException) // display an appropriate message
{
Console.WriteLine("You must enter a valid " +
"number and no other character!");
}
// If the user typed an invalid number out of the
// allowed range
// let him or her know and provide another chance
if ((ChoiceContainer < 1) ||
(ChoiceContainer > Container.Length))
Console.WriteLine("Invalid Choice - Try Again!");
} while ((ChoiceContainer < 1) ||
(ChoiceContainer > Container.Length));
}
internal void ChooseIngredient()
{
do
{
try
{
Console.WriteLine("Do you want an ingredient or not");
for (int i = 0; i < Ingredient.Length; i++)
Console.WriteLine("{0} - {1}",
i + 1,
Ingredient[i]);
Console.Write("Your Choice? ");
ChoiceIngredient = int.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("You must enter a valid " +
"number and no other character!");
}
if ((ChoiceIngredient < 1) ||
(ChoiceIngredient > Ingredient.Length))
Console.WriteLine("Invalid Choice - Try Again!");
} while ((ChoiceIngredient < 1) ||
(ChoiceIngredient > Ingredient.Length));
}
internal void SpecifyNumberOfScoops()
{
do
{
try
{
Console.Write("How many scoops(1, 2, or 3)? ");
Scoops = int.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("You must enter a valid number " +
"and no other character!");
}
if (Scoops < 1 || Scoops > 3)
Console.WriteLine("Invalid Choice - Try Again!");
} while (Scoops < 1 || Scoops > 3);
}
// This method is used to process a customer order
// It uses the values of the above methods
public void ProcessAnOrder()
{
// int ChoiceFlavor;
// int ChoiceContainer;
// int ChoiceIngredient;
decimal PriceIngredient, PriceScoop;
// Let the user know that this is a vending machine
Console.WriteLine("=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=");
Console.WriteLine("Ice Cream Vending Machine");
Console.WriteLine("-----------------------------------");
// Let the user select the components of the Ice Cream
Request Get = new Request(ChooseFlavor);
Get();
Console.WriteLine("-----------------------------------");
Get = new Request(ChooseContainer);
Get();
Console.WriteLine("-----------------------------------");
Get = new Request(ChooseIngredient);
Get();
Console.WriteLine("-----------------------------------");
Get = new Request(SpecifyNumberOfScoops);
Get();
Console.WriteLine("-----------------------------------");
// If the user selects an ingredient instead of "No Ingredient",
// add $0.50 to the order
if ((ChoiceIngredient == 2) ||
(ChoiceIngredient == 3) ||
(ChoiceIngredient == 4))
PriceIngredient = 0.50M;
else
PriceIngredient = 0.00M;
// Instead of multiplying a number scoops to a value,
// We will use an incremental value depending on
// the number of scoops
if (Scoops == 1)
PriceScoop = 0.65M;
else if (Scoops == 2)
PriceScoop = 1.05M;
else
PriceScoop = 1.55M;
// Calculate the total price of the Ice Cream
TotalPrice = BasePrice + PriceScoop + PriceIngredient;
// Create the Ice Cream...
// And display a receipt to the user
DisplayReceipt();
}
// This method is used to display a receipt to the user
internal void DisplayReceipt()
{
Console.WriteLine("\n=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=");
Console.WriteLine("Ice Cream Order");
Console.WriteLine("-----------------------------------");
Console.WriteLine("Flavor: {0}",
Flavor[ChoiceFlavor - 1]);
Console.WriteLine("Container: {0}",
Container[ChoiceContainer - 1]);
Console.WriteLine("Ingredient: {0}",
Ingredient[ChoiceIngredient - 1]);
Console.WriteLine("Scoops: {0}", Scoops);
Console.WriteLine("Total Price: {0:C}", TotalPrice);
Console.WriteLine("=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=\n");
}
internal void SaveOrder()
{
string strFilename;
Console.Write("Please enter your initials or the name " +
"we will use to remember your order: ");
strFilename = Console.ReadLine();
strFilename = strFilename + ".icr";
try
{
// Find out if the user entered a name of a file
// that is already in the machine
if (File.Exists(strFilename))
{
char answer;
FileStream stmIceCream =
new FileStream(strFilename, FileMode.Create);
BinaryWriter bnwIceCream =
new BinaryWriter(stmIceCream);
try
{
// If so, find out if the user wants to
// replace the old file
Console.WriteLine("The file you entered exists already.");
Console.Write("Do you want to replace it(y/n)?");
answer = char.Parse(Console.ReadLine());
// If the customer wants to replace it...
if (answer == 'y' || answer == 'Y')
{
// ... do so
Console.WriteLine("The former order with the same " +
"name will be replaced");
Console.WriteLine("\n=-= Ice Cream " +
"Vending Machine =-=");
Console.WriteLine(" Saving Order: {0}", strFilename);
bnwIceCream.Write(Flavor[ChoiceFlavor - 1]);
bnwIceCream.Write(Container[ChoiceContainer - 1]);
bnwIceCream.Write(Ingredient[ChoiceIngredient - 1]);
bnwIceCream.Write(Scoops);
bnwIceCream.Write(TotalPrice);
}
// If the customer wants to save the new order with
// a different name
else if (answer == 'n' || answer == 'N')
{
// Ask the user to enter a name to remember the order
Console.Write("Please enter a name we will use " +
"to remember this order: ");
strFilename = Console.ReadLine();
strFilename = strFilename + ".icr";
try
{
stmIceCream = new FileStream(strFilename,
FileMode.Create);
bnwIceCream = new BinaryWriter(stmIceCream);
Console.WriteLine("\n=-= Ice Cream " +
"Vending Machine =-=");
Console.WriteLine(" Saving Order: {0}",
strFilename);
bnwIceCream.Write(Flavor[ChoiceFlavor - 1]);
bnwIceCream.Write(Container[ChoiceContainer - 1]);
bnwIceCream.Write(Ingredient[ChoiceIngredient - 1]);
bnwIceCream.Write(Scoops);
bnwIceCream.Write(TotalPrice);
}
catch (IOException)
{
Console.Write("\nThe file you wanted us to " +
"create exists already. ");
Console.WriteLine("In case it was registered " +
"by a different customer, " +
"we will not delete it.");
}
}
else
Console.WriteLine("Invalid Answer - We will close");
}
catch (IOException)
{
Console.Write("\nThat file exists already. ");
Console.WriteLine("We need to preserve it just in " +
"case another customer will require it.");
}
finally
{
bnwIceCream.Close();
stmIceCream.Close();
}
}
else
{
FileStream stmIceCream =
new FileStream(strFilename, FileMode.Create);
BinaryWriter bnwIceCream =
new BinaryWriter(stmIceCream);
try
{
Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
Console.WriteLine(" Saving Order: {0}", strFilename);
bnwIceCream.Write(Flavor[ChoiceFlavor - 1]);
bnwIceCream.Write(Container[ChoiceContainer - 1]);
bnwIceCream.Write(Ingredient[ChoiceIngredient - 1]);
bnwIceCream.Write(Scoops);
bnwIceCream.Write(TotalPrice);
}
finally
{
bnwIceCream.Close();
stmIceCream.Close();
}
}
}
catch (IOException ex)
{
Console.WriteLine("\nError: " + ex.Message);
Console.WriteLine("Operation Canceled: The file you want " +
"to create exists already.");
}
}
internal void OpenOrder()
{
string strFilename;
string SelectedFlavor;
string SelectedContainer;
string SelectedIngredient;
// Ask the user to enter a name of a previously saved order
Console.Write("Please enter the name you previously " +
"gave to remember your order: ");
strFilename = Console.ReadLine();
strFilename = strFilename + ".icr";
try
{
FileStream stmIceCream =
new FileStream(strFilename, FileMode.Open);
BinaryReader bnrIceCream =
new BinaryReader(stmIceCream);
try
{
// Find out if this order was previously saved in the machine
if (File.Exists(strFilename))
{
// If so, open it
SelectedFlavor = bnrIceCream.ReadString();
SelectedContainer = bnrIceCream.ReadString();
SelectedIngredient = bnrIceCream.ReadString();
Scoops = bnrIceCream.ReadInt32();
TotalPrice = bnrIceCream.ReadDecimal();
// And display it to the user
Console.WriteLine("\n=-= Ice Cream Vending Machine =-=");
Console.WriteLine(" Previous Order: {0}", strFilename);
Console.WriteLine("Flavor: {0}", SelectedFlavor);
Console.WriteLine("Container: {0}", SelectedContainer);
Console.WriteLine("Ingredient: {0}", SelectedIngredient);
Console.WriteLine("Scoops: {0}", Scoops);
Console.WriteLine("Total Price: {0:C}\n", TotalPrice);
}
else
Console.WriteLine("The name you entered is not " +
"registered in our previous orders");
}
finally
{
bnrIceCream.Close();
stmIceCream.Close();
}
}
catch (FileNotFoundException ex)
{
Console.Write("\nError: " + ex.Message);
Console.WriteLine("It is unlikely that the file exists in " +
"our machine's register.");
}
}
}
}
- Exercise the application and test it
- Close the DOS window
In its high level of support for file processing, the .NET
Framework provides the FileInfo class. This class is equipped to handle
all types of file-related operations including creating, copying, moving,
renaming, or deleting a file. FileInfo is based on the FileSystemInfo
class that provides information on characteristics of a file.
|
Practical Learning: Introducing File Information
|
|
- Start a new Console Application named WattsALoan2
- To take advantage of the Visual Basic rich library, in the Solution
Explorer, under WattsALoan2, right-click References and click Add Reference
- In the Add Reference dialog box, click the .NET tab and click
Microsoft.VisualBasic
- Click OK
- Change the Program.cs file as follows:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
namespace WattsALoan1
{
public class Program
{
static int Main(string[] args)
{
string EmployerName, ApplicantName;
string HomePhone, WorkPhone;
double LoanAmount = 0.00D, InterestRate = 0.0D;
double MonthlyPayment = 0.00D, Periods = 0D;
Console.WriteLine(" -=- Car Loan Application -=-");
Console.WriteLine("Enter the following pieces " +
"of information\n");
Console.WriteLine("Applicant Information");
Console.Write("Full Name: ");
ApplicantName = Console.ReadLine();
Console.Write("Employer Name: ");
EmployerName = Console.ReadLine();
Console.Write("Home Phone: ");
HomePhone = Console.ReadLine();
Console.Write("Work Phone: ");
WorkPhone = Console.ReadLine();
Console.WriteLine("Loan Estimation");
try
{
Console.Write("Amount of Loan: ");
LoanAmount = double.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("Invalid Loan Amount");
}
try
{
Console.Write("Interest Rate(0 to 100): ");
InterestRate = double.Parse(Console.ReadLine()) / 100;
}
catch (FormatException)
{
Console.WriteLine("Invalid Interest Rate");
}
try
{
Console.Write("Number of Months: ");
Periods = double.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("Invalid Number of Months");
}
try
{
MonthlyPayment =
Microsoft.VisualBasic.Financial.Pmt(InterestRate / 12,
Periods, -LoanAmount,
0, Microsoft.VisualBasic.DueDate.BegOfPeriod);
}
catch (ArgumentException)
{
Console.WriteLine("Some invalid values were provided\n");
}
Console.WriteLine();
Console.WriteLine(" -=-=-=-=-=-=-=-=-=-=-=-=-=-=");
Console.WriteLine(" -=- Car Loan Application -=-");
Console.WriteLine(" -=-=-=-=-=-=-=-=-=-=-=-=-=-=");
Console.WriteLine("Applicant Information");
Console.WriteLine("Full Name: {0}", ApplicantName);
Console.WriteLine("Employer Name: {0}", EmployerName);
Console.WriteLine("Home Phone: {0}", HomePhone);
Console.WriteLine("Work Phone: {0}", WorkPhone);
Console.WriteLine("Loan Estimation");
Console.WriteLine("Loan Amount: {0:C}", LoanAmount);
Console.WriteLine("Interest Rate: {0:P}", InterestRate);
Console.WriteLine("Number of Months: {0:F}", Periods);
Console.WriteLine("Monthly Payment: {0:C}\n", MonthlyPayment);
}
}
}
- Execute the application and test it. Here is an example:
-=- Car Loan Application -=-
Enter the following pieces of information
Applicant Information
Full Name: James Watts
Employer Name: Wattson Enterprises
Home Phone: (202) 374-4738
Work Phone: (301) 894-4789
Loan Estimation
Amount of Loan: 12500
Interest Rate(0 to 100): 10.25
Number of Months: 48
-=-=-=-=-=-=-=-=-=-=-=-=-=-=
-=- Car Loan Application -=-
-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Applicant Information
Full Name: James Watts
Employer Name: Wattson Enterprises
Home Phone: (202) 374-4738
Work Phone: (301) 894-4789
Loan Estimation
Loan Amount: $12,500.00
Interest Rate: 10.25 %
Number of Months: 48.00
Monthly Payment: $315.84
Press any key to continue...
- Close the DOS window
The FileInfo class is equipped with one constructor
whose syntax is:
public FileInfo(string fileName);
This constructor takes as argument the name of a file or its
complete path. If you provide only the name of the file, the compiler would
consider the same directory of its project. Here is an example:
FileInfo fleMembers = new FileInfo("First.txt");
Alternatively, if you want, you can provide any valid
directory you have access to. In this case, you should provide the complete
path.
The FileInfo constructor is mostly meant only to
indicate that you want to use a file, whether it exists already or it would be
created. Based on this, if you execute an application that has only a
FileInfo object created using the constructor as done above, nothing would
happen.
To create a file, you have various alternatives. If you want
to create one without writing anything in it, which implies creating an empty
file, you can call the FileInfo.Create() method. Its syntax is:
public FileStream Create();
This method simply creates an empty file. Here is an example
of calling it:
using System;
using System.IO;
public class Program
{
static int Main(string[] args)
{
var fleMembers = new FileInfo("First.txt");
fleMembers.Create();
return 0;
}
}
The FileInfo.Create() method returns a FileStream
object. You can use this returned value to write any type of value into the
file, including text. If you want to create a file that contains text, an
alternative is to call the FileInfo.CreateText() method. Its syntax is:
public StreamWriter CreateText();
This method directly returns a StreamWriter object.
You can use this returned object to write text to the file.
When you call the FileInfo.Create() or the
FileInfo.CreateText() method, if the file passed as argument, or as the file
in the path of the argument, exists already, it would be deleted and a new one
would be created with the same name. This can cause the right file to be
deleted. Therefore, before creating a file, you may need to check whether it
exists already. To do this, you can check the value of the Boolean
FileInfo.Exists property. This property holds a true value if the
file exists already and it holds a false value if the file doesn't exist
or it doesn't exist in the path.
Here is an example of checking the existence of a file:
using System;
using System.IO;
public class Program
{
static int Main(string[] args)
{
var fleMembers = new FileInfo("First.txt");
if (fleMembers.Exists == true)
return 0;
else
fleMembers.Create();
return 0;
}
}
As mentioned earlier, the FileInfo.Create() method
returns a FileStream object. You can use this to specify the type of
operation that would be allowed on the file.
To write normal text to a file, you can first call the
FileInfo.CreateText() method. This method returns a StreamWriter
object. The StreamWriter class is based on the TextWriter class
that is equipped with the Write() and the WriteLine() methods used
to write values to a file. The Write() method writes text on a line and
keeps the caret on the same line. The WriteLine() method writes a line of
text and moves the caret to the next line.
After writing to a file, you should close the
StreamWriter object to free the resources it was using during its
operation(s).
|
Practical Learning: Writing to a File
|
|
- To allow the user to create a new employee, change the file as follows:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
namespace WattsALoan2
{
class Program
{
private static void CreateNewEmployee()
{
string employeeNumber, employeeName;
FileInfo fleEmployees = new FileInfo("Employees.txt");
StreamWriter swrEmployees = fleEmployees.CreateText();
try
{
Console.WriteLine("Hiring New Employee");
Console.Write("Enter Employee Number as 00-000: ");
employeeNumber = Console.ReadLine();
Console.Write("Enter Employee Name: ");
employeeName = Console.ReadLine();
swrEmployees.WriteLine(employeeNumber);
swrEmployees.WriteLine(employeeName);
}
finally
{
swrEmployees.Flush();
swrEmployees.Close();
}
}
static int Main(string[] args)
{
try
{
Console.Write("Do you want to hire a new " +
"employee(0=No/1=Yes)? ");
int answer = int.Parse(Console.ReadLine());
if (answer == 1)
CreateNewEmployee();
}
catch (FormatException)
{
Console.WriteLine("That was an invalid answer!\n");
}
string EmployerName, ApplicantName;
string HomePhone, WorkPhone;
double LoanAmount = 0.00D, InterestRate = 0.0D;
double MonthlyPayment = 0.00D, Periods = 0D;
. . . No Change
return 0;
}
}
}
- Execute the application. Here is an example:
Do you want to hire a new employee(0=No/1=Yes)? 1
Hiring New Employee
Enter Employee Number as 00-000: 44-228
Enter Employee Name: Johnny Olney
- Close the DOS window
You may have created a text-based file and written to it. If
you open such a file and find out that a piece of information is missing, you
can add that information to the end of the file. To do this, you can call the
FileInfo.AppenText() method. Its syntax is:
public StreamWriter AppendText();
When calling this method, you can retrieve the
StreamWriter object that it returns, then use that object to add new
information to the file.
|
Practical Learning: Appending to a File
|
|
- To allow the user to add more employees to the file that holds their
names, change the file as follows:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
namespace WattsALoan2
{
public class Program
{
private static void CreateNewEmployee()
{
string employeeNumber, employeeName;
FileInfo fleEmployees = new FileInfo("Employees.txt");
StreamWriter swrEmployees = null;
// If the file exists already, then add the new employee to it
if (fleEmployees.Exists == true)
swrEmployees = fleEmployees.AppendText();
else // Otherwise, create a new file
swrEmployees = fleEmployees.CreateText();
try
{
Console.WriteLine("Hiring New Employee");
Console.Write("Enter Employee Number as 00-000: ");
employeeNumber = Console.ReadLine();
Console.Write("Enter Employee Name: ");
employeeName = Console.ReadLine();
swrEmployees.WriteLine(employeeNumber);
swrEmployees.WriteLine(employeeName);
}
finally
{
swrEmployees.Flush();
swrEmployees.Close();
}
}
static void Main(string[] args)
{
. . . No Change
}
}
}
- Execute the application
- Type y to create an employee. Here is an example:
Do you want to hire a new employee(0=No/1=Yes)? 1
Hiring New Employee
Enter Employee Number as 00-000: 72-604
Enter Employee Name: Ernest Barzan
- Close the DOS window
|
|
