Techniques of Using Exception Handling
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Techniques of Using Exception Handling |
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Introduction |
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As mentioned in the previous lesson, the Exception class is equipped with a Message property that holds a string about the error that occurred. The message of this property may not be particularly useful to a user. Fortunately, you can create your own message and pass it to the Exception class. To be able to receive custom messages, the Exception class provides the following constructor: public Exception(string message); |
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When a bad behavior occurs in your application, the program is said to throw an exception. Your job is to know, as much as possible, when and why this would happen. In the previous lesson and in the above section, we saw that, when an application throws an exception, you could display your own message. To effectively address a particular exception, you need to identify the (exact, if possible) section of code where the exception would occur and you should know why the error would be produced. After identifying the area in code where an exception is likely to occur, you can further customize the behavior of your application. |
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To customize the throwing of an exception, in the section of code where you are anticipating the error, type the throw keyword followed by a new instance of the Exception class (or one of its derived classes) using the constructor that takes a string. Here is an example:
Practical Learning: Using Exceptionsusing System;
class Program
{
static int Main()
{
double Operand1, Operand2;
double Result = 0.00;
char Operator;
Console.WriteLine("This program allows you to perform an operation on two numbers");
try
{
Console.Write("Enter a number: ");
Operand1 = double.Parse(Console.ReadLine());
Console.Write("Enter an operator: ");
Operator = char.Parse(Console.ReadLine());
Console.Write("Enter a number: ");
Operand2 = double.Parse(Console.ReadLine());
if (Operator != '+' && Operator != '-' && Operator != '*' && Operator != '/')
throw new Exception(Operator.ToString());
switch (Operator)
{
case '+':
Result = Operand1 + Operand2;
break;
case '-':
Result = Operand1 - Operand2;
break;
case '*':
Result = Operand1 * Operand2;
break;
case '/':
Result = Operand1 / Operand2;
break;
default:
Console.WriteLine("Bad Operation");
break;
}
Console.WriteLine("\n{0} {1} {2} = {3}", Operand1, Operator, Operand2, Result);
}
catch (Exception ex)
{
Console.WriteLine("\nOperation Error: {0} is not a valid operator", ex.Message);
}
return 0;
}
}
Here is an example of running the program:
This program allows you to perform an operation on two numbers Enter a number: 124.55 Enter an operator: & Enter a number: 36.85 Operation Error: & is not a valid operator Press any key to continue . . .
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using System;
namespace RealEstate5
{
public enum PropertyType
{
Unknown,
SingleFamily,
Townhouse,
Condominium
}
class PropertyListing
{
. . . No Change
public void CreateListing()
{
. . . No Change
switch ((PropertyType)propType)
{
case PropertyType.SingleFamily:
Type = PropertyType.SingleFamily;
try
{
Console.Write("\nHow many stories (levels)? ");
House.Stories = short.Parse(Console.ReadLine());
if (House.Stories < 1)
{
House.Stories = 1;
throw new OverflowException("The number of stories must be positive");
}
}
catch (OverflowException ex)
{
Console.WriteLine(ex.Message);
}
. . . No Change
break;
case PropertyType.Townhouse:
Type = PropertyType.Townhouse;
try
{
Console.Write("\nHow many stories (levels)? ");
House.Stories = short.Parse(Console.ReadLine());
if (House.Stories < 1)
{
House.Stories = 1;
throw new OverflowException("The number of stories must be positive");
}
}
catch (OverflowException ex)
{
Console.WriteLine(ex.Message);
}
. . . No Change
}
. . . No Change
}
public void ShowProperty()
{
. . . No Change
}
}
}
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=//= Altair Realty =//= -=- Property Creation -=- Types of Properties 1. Single Family 2. Townhouse 3. Condominium 4. Don't Know Enter Type of Property: 2 Enter Property #: 463864 Properties Conditions 1. Excellent 2. Good (may need minor repair) 3. Needs Repair 4. In Bad Shape (property needs major repair or rebuild) Enter Property Condition: 3 How many stories (levels)? -3 The number of levels must be positive Does it have an indoor car garage (y/n): G Is the basement finished(y/n): K How many bedrooms? -4 How many bathrooms? -2 Year built: 2994 Property Value: 425885 ================================== =//=//= Altair Realty =//=//= -=-=-=- Properties Listing -=-=-=- ---------------------------------- Property #: 463864 Property Type: Townhouse Stories: 1 Has Indoor Car Garage: False Finished Basement: False Condition: NeedsRepair Bedrooms: 1 Bathrooms: 0.00 Year Built: 2994 Market Value: $425,885.00 Press any key to continue . . . |
In the examples above, when we anticipated some type of problem, we instructed the compiler to use our default catch section. We left it up to the compiler to find out when there was a problem and we provided a catch section to deal with it. A method with numerous or complex operations and requests can also produce different types of errors. With such a type of program, you should be able to face different problems and deal with them individually, each by its own kind. To do this, you can create different catch sections, each made for a particular error. The formula used would be:
try {
// Code to Try
}
catch(Arg1)
{
// One Exception
}
catch(Arg2)
{
// Another Exception
}
The compiler would proceed in a top-down:
Multiple catches are written if or when a try block is expected to throw different types of errors. Once again, consider the previous program. That program works fine as long as the user types a valid sequence of values made of a number, a valid arithmetic operator, and a number. Anything else, such as an invalid number, an unexpected operator, or a wrong sequence (such as a number then another number instead of an operator), would cause an error. Obviously various bad things could happen when this program is running. To handle the exceptions that this program could produce, you can start with the most likely problem that would occur. Trusting that a user is able to provide the two numbers that are requested, it is possible that a user would type an invalid operator. For example, for this program we will perform only the addition (+), the subtraction(-), the multiplication(*), and the division(/). Therefore, we will first validate the operator. This can be done as follows:
using System;
class Program
{
static int Main()
{
double Operand1, Operand2;
double Result = 0.00;
char Operator;
Console.WriteLine("This program allows you to perform an operation on two numbers");
try
{
Console.Write("Enter a number: ");
Operand1 = double.Parse(Console.ReadLine());
Console.Write("Enter an operator: ");
Operator = char.Parse(Console.ReadLine());
Console.Write("Enter a number: ");
Operand2 = double.Parse(Console.ReadLine());
if (Operator != '+' &&
Operator != '-' &&
Operator != '*' &&
Operator != '/')
throw new Exception(Operator.ToString());
switch (Operator)
{
case '+':
Result = Operand1 + Operand2;
break;
case '-':
Result = Operand1 - Operand2;
break;
case '*':
Result = Operand1 * Operand2;
break;
case '/':
Result = Operand1 / Operand2;
break;
default:
Console.WriteLine("Bad Operation");
break;
}
Console.WriteLine("\n{0} {1} {2} = {3}", Operand1, Operator, Operand2, Result);
}
catch (Exception ex)
{
Console.WriteLine("\nOperation Error: {0} is not a valid operator", ex.Message);
}
return 0;
}
}
When this program runs, if the user provides a valid number followed by a wrong operator, we call the Exception(string message) constructor and pass it a string converted from the character that was typed.
Imagine that the user wants to perform a division. You need to tell the compiler what to do if the user enters the denominator as 0 (or 0.00). If this happens, probably the best option is to display a message and get out. Fortunately, the .NET Framework provides the DivideByZeroException class to deal with an exception caused by division by zero. As done with the message passed to the Exception class, you can compose your own message and pass it to the DivideByZeroException(string message) constructor.
Here is an example that catches two types of exceptions:
using System;
class Program
{
static int Main()
{
double Operand1, Operand2;
double Result = 0.00;
char Operator;
Console.WriteLine("This program allows you to perform an operation on two numbers");
try
{
Console.Write("Enter a number: ");
Operand1 = double.Parse(Console.ReadLine());
Console.Write("Enter an operator: ");
Operator = char.Parse(Console.ReadLine());
Console.Write("Enter a number: ");
Operand2 = double.Parse(Console.ReadLine());
if (Operator != '+' &&
Operator != '-' &&
Operator != '*' &&
Operator != '/')
throw new Exception(Operator.ToString());
if (Operator == '/') if (Operand2 == 0)
throw new DivideByZeroException("Division by zero is not allowed");
switch (Operator)
{
case '+':
Result = Operand1 + Operand2;
break;
case '-':
Result = Operand1 - Operand2;
break;
case '*':
Result = Operand1 * Operand2;
break;
case '/':
Result = Operand1 / Operand2;
break;
default:
Console.WriteLine("Bad Operation");
break;
}
Console.WriteLine("\n{0} {1} {2} = {3}", Operand1, Operator, Operand2, Result);
}
catch (DivideByZeroException ex)
{
Console.WriteLine(ex.Message);
}
catch (Exception ex)
{
Console.WriteLine("\nOperation Error: {0} is not a valid operator", ex.Message);
}
return 0;
}
}
When running this program, if the user types a wrong operator, the compiler gets out of the try block and looks for a catch that takes an Exception as argument. It finds the second and executes it. If the user enters the right values (a number, an operator, and another number), then the compiler finds out if the operator entered was a forward slash “/” used to perform a division. If the user wants to perform a division, the compiler finds out if the second operand, the denominator, is 0. If it is, we create a DivideByZeroException instance and pass our own message to it. Based on this exception, the compiler gets out of the try block and starts looking for a catch block that takes a DivideByZeroException argument. It finds it in the first catch. Therefore, the compiler executes it.
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using System;
namespace RealEstate5
{
public enum PropertyType
{
Unknown,
SingleFamily,
Townhouse,
Condominium
}
class PropertyListing
{
private Property prop;
private HouseType hse;
private Condominium cond;
private PropertyType tp;
public Property ListProperty
{
get { return prop; }
set { prop = value; }
}
public HouseType House
{
get { return hse; }
set { hse = value; }
}
public Condominium Condo
{
get { return cond; }
set { cond = value; }
}
public PropertyType Type
{
get { return tp; }
set { tp = value; }
}
public PropertyListing()
{
prop = new Property();
hse = new HouseType();
cond = new Condominium();
}
public void CreateListing()
{
char answer = 'n';
short propType = 1;
short condition = 1;
Console.WriteLine(" =//= Altair Realty =//=");
Console.WriteLine("-=- Property Creation -=-");
try
{
Console.WriteLine("\nTypes of Properties");
Console.WriteLine("1. Single Family");
Console.WriteLine("2. Townhouse");
Console.WriteLine("3. Condominium");
Console.WriteLine("4. Don't Know");
Console.Write("Enter Type of Property: ");
propType = short.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("The value you entered is not a valid number");
}
catch (Exception)
{
Console.WriteLine("Something bad happened and we don't like it");
}
Console.Write("\nEnter Property #: ");
ListProperty.PropertyNumber = Console.ReadLine();
try
{
Console.WriteLine("\nProperties Conditions");
Console.WriteLine("1. Excellent");
Console.WriteLine("2. Good (may need minor repair)");
Console.WriteLine("3. Needs Repair");
Console.Write("4. In Bad Shape (property needs ");
Console.WriteLine("major repair or rebuild)");
Console.Write("Enter Property Condition: ");
condition = short.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("The value you typed for the property condition is not good");
}
catch (Exception)
{
Console.WriteLine("Something unacceptable has just happened");
}
if (condition == 1)
ListProperty.Condition = PropertyCondition.Excellent;
else if (condition == 2)
ListProperty.Condition = PropertyCondition.Good;
else if (condition == 3)
ListProperty.Condition = PropertyCondition.NeedsRepair;
else if (condition == 4)
ListProperty.Condition = PropertyCondition.BadShape;
else
ListProperty.Condition = PropertyCondition.Unknown;
switch ((PropertyType)propType)
{
case PropertyType.SingleFamily:
Type = PropertyType.SingleFamily;
try
{
Console.Write("\nHow many stories (levels)? ");
House.Stories = short.Parse(Console.ReadLine());
if (House.Stories < 1)
{
House.Stories = 1;
throw new OverflowException("The number of levels must be positive");
}
}
catch (OverflowException ex)
{
Console.WriteLine(ex.Message);
}
catch (FormatException)
{
Console.WriteLine("The number you entered for the stories is not allowed");
}
catch (Exception)
{
Console.WriteLine("This is one of those abnormal behaviors");
}
try
{
Console.Write("Does it have an indoor car garage (y/n): ");
answer = char.Parse(Console.ReadLine());
if ((answer == 'y') || (answer == 'Y'))
House.IndoorGarage = true;
else
House.IndoorGarage = false;
}
catch (FormatException)
{
Console.WriteLine("Invalid Indoor Car Garage Answer");
}
try
{
Console.Write("Is the basement finished(y/n): ");
answer = char.Parse(Console.ReadLine());
if ((answer == 'y') || (answer == 'Y'))
House.FinishedBasement = true;
else
House.FinishedBasement = false;
}
catch (FormatException)
{
Console.WriteLine("Invalid Basement Answer");
}
break;
case PropertyType.Townhouse:
Type = PropertyType.Townhouse;
try
{
Console.Write("\nHow many stories (levels)? ");
House.Stories = short.Parse(Console.ReadLine());
if (House.Stories < 1)
{
House.Stories = 1;
throw new OverflowException("The number of levels must be positive");
}
}
catch (OverflowException ex)
{
Console.WriteLine(ex.Message);
}
catch (FormatException)
{
Console.WriteLine("The number you entered for the stories is not allowed");
}
catch (Exception)
{
Console.WriteLine("This is one of those abnormal behaviors");
}
Console.Write("Does it have an indoor car garage (y/n): ");
answer = char.Parse(Console.ReadLine());
if ((answer == 'y') || (answer == 'Y'))
House.IndoorGarage = true;
else
House.IndoorGarage = false;
Console.Write("Is the basement finished(y/n): ");
answer = char.Parse(Console.ReadLine());
if ((answer == 'y') || (answer == 'Y'))
House.FinishedBasement = true;
else
House.FinishedBasement = false;
break;
case PropertyType.Condominium:
Type = PropertyType.Condominium;
Console.Write("\nIs the building accessible to handicapped (y/n): ");
answer = char.Parse(Console.ReadLine());
if ((answer == 'y') || (answer == 'Y'))
Condo.HandicapAccessible = true;
else
Condo.HandicapAccessible = false;
break;
default:
Type = PropertyType.Unknown;
break;
}
try
{
Console.Write("\nHow many bedrooms? ");
ListProperty.Bedrooms = short.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("The value you entered for the number of bedrooms is not acceptable");
}
catch (Exception)
{
Console.WriteLine("The program has decided to stop");
}
try
{
Console.Write("How many bathrooms? ");
ListProperty.Bathrooms = float.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("The value you decided to enter for the bedrooms is rejected");
}
catch (Exception)
{
Console.WriteLine("The computer doesn't like what is going on");
}
try
{
Console.Write("Year built: ");
ListProperty.YearBuilt = int.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("You didn't enter a valid number for the year built");
}
catch (Exception)
{
Console.WriteLine("Whatever, whatever, whatever");
}
try
{
Console.Write("Property Value: ");
ListProperty.Value = decimal.Parse(Console.ReadLine());
}
catch (FormatException)
{
Console.WriteLine("The value of a property must be a good decimal number");
}
catch (Exception)
{
Console.WriteLine("This is where the application draws the line: it stops!");
}
}
public void ShowProperty()
{
Console.WriteLine("==================================");
Console.WriteLine(" =//=//= Altair Realty =//=//=");
Console.WriteLine("-=-=-=- Properties Listing -=-=-=-");
Console.WriteLine("----------------------------------");
Console.WriteLine("Property #: {0}",
ListProperty.PropertyNumber);
Console.WriteLine("Property Type: {0}", Type);
switch (Type)
{
case PropertyType.SingleFamily:
case PropertyType.Townhouse:
Type = PropertyType.SingleFamily;
Console.WriteLine("Stories: {0}",
House.Stories);
Console.WriteLine("Has Indoor Car Garage: {0}",
House.IndoorGarage);
Console.WriteLine("Finished Basement: {0}",
House.FinishedBasement);
break;
case PropertyType.Condominium:
Console.WriteLine("Handicapped Accessible Building: {0}",
Condo.HandicapAccessible);
break;
}
Console.WriteLine("Condition: {0}", ListProperty.Condition);
Console.WriteLine("Bedrooms: {0}", ListProperty.Bedrooms);
Console.WriteLine("Bathrooms: {0:F}", ListProperty.Bathrooms);
Console.WriteLine("Year Built: {0}", ListProperty.YearBuilt);
Console.WriteLine("Market Value: {0:C}", ListProperty.Value);
}
}
}
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=//= Altair Realty =//= -=- Property Creation -=- Types of Properties 1. Single Family 2. Townhouse 3. Condominium 4. Don't Know Enter Type of Property: 1 Enter Property #: 228046 Properties Conditions 1. Excellent 2. Good (may need minor repair) 3. Needs Repair 4. In Bad Shape (property needs major repair or rebuild) Enter Property Condition: 4 How many stories (levels)? -5 The number of levels must be positive Does it have an indoor car garage (y/n): y Is the basement finished(y/n): Not at all Invalid Basement Answer How many bedrooms? Apparently 3 or 4 The value you entered for the number of bedrooms is not acceptable How many bathrooms? 1 can flush, the owner is working on another The value you decided to enter for the bedrooms is rejected Year built: Around 1962 You didn't enter a valid number for the year built Property Value: A little over 420000 The value of a property must be an good decimal number ================================== =//=//= Altair Realty =//=//= -=-=-=- Properties Listing -=-=-=- ---------------------------------- Property #: 228046 Property Type: SingleFamily Stories: 1 Has Indoor Car Garage: True Finished Basement: False Condition: BadShape Bedrooms: 1 Bathrooms: 0.00 Year Built: 0 Market Value: $0.00 Press any key to continue . . . |
The calculator simulator we have studied so far performs a division as one of its assignments. We learned that, in order to perform any operation, the compiler must first make sure that the user has entered a valid operator. Provided the operator is one of those we are expecting, we also must make sure that the user typed valid numbers. Even if these two criteria are met, it was possible that the user enter 0 for the denominator. The block that is used to check for a non-zero denominator depends on the exception that validates the operators. The exception that could result from a zero denominator depends on the user first entering a valid number for the denominator.
You can create an exception inside of another. This is referred to as nesting an exception. This is done by applying the same techniques we used to nest conditional statements. This means that you can write an exception that depends on, or is subject to, another exception. To nest an exception, write a try block in the body of the parent exception. The nested try block must be followed by its own catch(es) clause. To effectively handle the exception, make sure you include an appropriate throw in the try block. Here is an example:
using System;
class Program
{
static int Main()
{
double Operand1, Operand2;
double Result = 0.00;
char Operator;
Console.WriteLine("This program allows you to perform an operation on two numbers");
try
{
Console.Write("Enter a number: ");
Operand1 = double.Parse(Console.ReadLine());
Console.Write("Enter an operator: ");
Operator = char.Parse(Console.ReadLine());
Console.Write("Enter a number: ");
Operand2 = double.Parse(Console.ReadLine());
if (Operator != '+' &&
Operator != '-' &&
Operator != '*' &&
Operator != '/')
throw new Exception(Operator.ToString());
switch (Operator)
{
case '+':
Result = Operand1 + Operand2;
Console.WriteLine("\n{0} + {1} = {2}", Operand1, Operand2, Result);
break;
case '-':
Result = Operand1 - Operand2;
Console.WriteLine("\n{0} - {1} = {2}", Operand1, Operand2, Result);
break;
case '*':
Result = Operand1 * Operand2;
Console.WriteLine("\n{0} * {1} = {2}", Operand1, Operand2, Result);
break;
case '/':
// The following exception is nested in the previous try
try
{
if (Operand2 == 0)
throw new DivideByZeroException("Division by zero is not allowed");
Result = Operand1 / Operand2;
Console.WriteLine("\n{0} / {1} = {2}", Operand1, Operand2, Result);
}
catch (DivideByZeroException ex)
{
Console.WriteLine(ex.Message);
}
break;
}
}
catch (Exception ex)
{
Console.WriteLine("\nOperation Error: {0} is not a valid operator", ex.Message);
}
return 0;
}
}
Here is an example of running the program:
This program allows you to perform an operation on two numbers Enter a number: 324.53 Enter an operator: / Enter a number: 0 Division by zero is not allowed Press any key to continue . . .
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Exceptions and Methods |
One of the most effective techniques used to deal with code is to isolate assignments. We learned this when studying methods of classes. For example, the switch statement that was performing the operations in the “normal” version of our program can be written as follows:
using System;
class Program
{
static int Main()
{
double Number1, Number2;
double Result = 0.00;
char Operator;
Console.WriteLine("This program allows you to perform an operation on two numbers");
try
{
Console.WriteLine("To proceed, enter");
Console.Write("First Number: ");
Number1 = double.Parse(Console.ReadLine());
Console.Write("An Operator (+, -, * or /): ");
Operator = char.Parse(Console.ReadLine());
if (Operator != '+' && Operator != '-' &&
Operator != '*' && Operator != '/')
throw new Exception(Operator.ToString());
Console.Write("Second Number: ");
Number2 = double.Parse(Console.ReadLine());
if (Operator == '/')
if (Number2 == 0)
throw new DivideByZeroException("Division by zero is not allowed");
Result = Calculator(Number1, Number2, Operator);
Console.WriteLine("\n{0} {1} {2} = {3}", Number1, Operator, Number2, Result);
}
catch (FormatException)
{
Console.WriteLine("The number you typed is not valid");
}
catch (DivideByZeroException ex)
{
Console.WriteLine(ex.Message);
}
catch (Exception ex)
{
Console.WriteLine("\nOperation Error: {0} is not a valid operator", ex.Message);
}
return 0;
}
static double Calculator(double Value1, double Value2, char Symbol)
{
double Result = 0.00;
switch (Symbol)
{
case '+':
Result = Value1 + Value2;
break;
case '-':
Result = Value1 - Value2;
break;
case '*':
Result = Value1 * Value2;
break;
case '/':
Result = Value1 / Value2;
break;
}
return Result;
}
}
Here is one example of running the program:
This program allows you to perform an operation on two numbers To proceed, enter First Number: 248.84 An Operator (+, -, * or /): * Second Number: 57.93 248.84 * 57.93 = 14415.3012 Press any key to continue . . .
Here is another example of running the program:
This program allows you to perform an operation on two numbers To proceed, enter First Number: 12.55 An Operator (+, -, * or /): [ Operation Error: [ is not a valid operator Press any key to continue . . .
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You can still use regular methods along with methods that handle exceptions. As done in Main(), any method of a program can take care of its own exceptions that would occur in its body. Here is an example of an exception handled in a method: |
using System;
class Program
{
static int Main()
{
double Number1, Number2;
double Result = 0.00;
char Operator;
Console.WriteLine("This program allows you to perform an operation on two numbers");
try
{
Console.WriteLine("To proceed, enter");
Console.Write("First Number: ");
Number1 = double.Parse(Console.ReadLine());
Console.Write("An Operator (+, -, * or /): ");
Operator = char.Parse(Console.ReadLine());
if (Operator != '+' && Operator != '-' &&
Operator != '*' && Operator != '/')
throw new Exception(Operator.ToString());
Console.Write("Second Number: ");
Number2 = double.Parse(Console.ReadLine());
Result = Calculator(Number1, Number2, Operator);
}
catch (FormatException)
{
Console.WriteLine("The number you typed is not valid");
}
catch (Exception ex)
{
Console.WriteLine("\nOperation Error: {0} is not a valid operator", ex.Message);
}
return 0;
}
static double Calculator(double Value1, double Value2, char Symbol)
{
double Result = 0.00;
switch (Symbol)
{
case '+':
Result = Value1 + Value2;
Console.WriteLine("\n{0} + {1} = {2}", Value1, Value2, Result);
break;
case '-':
Result = Value1 - Value2;
Console.WriteLine("\n{0} - {1} = {2}", Value1, Value2, Result);
break;
case '*':
Result = Value1 * Value2;
Console.WriteLine("\n{0} * {1} = {2}", Value1, Value2, Result);
break;
case '/':
// The following exception is nested in the previous try
try
{
if (Value2 == 0)
throw new DivideByZeroException("Division by zero is not allowed");
Result = Value1 / Value2;
Console.WriteLine("\n{0} / {1} = {2}", Value1, Value2, Result);
}
catch (DivideByZeroException ex)
{
Console.WriteLine(ex.Message);
}
break;
}
return Result;
}
}
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Isolating assignments and handing them to method is an important matter in the area of application programming. Consider a program that handles a simple exception such as this one: |
using System;
class Program
{
static int Main()
{
double Number1, Number2;
double Result = 0.00;
char Operator = '/';
Console.WriteLine("This program allows you to perform a division of two numbers");
try
{
Console.Write("Enter a number: ");
Number1 = double.Parse(Console.ReadLine());
Console.Write("Enter a number: ");
Number2 = double.Parse(Console.ReadLine());
if (Number2 == 0)
throw new DivideByZeroException("Division by zero is not allowed");
Result = Number1 / Number2;
Console.WriteLine("\n{0} / {1} = {2}", Number1, Number2, Result);
}
catch (DivideByZeroException ex)
{
Console.WriteLine(ex.Message);
}
return 0;
}
}
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One of the ways you can use methods in exception routines is to have a central method that receives variables, and sends them to other external methods. The external method tests the value of a variable. If an exception occurs, the external method displays or sends a throw. This throw can be picked up by the method that sent the error. Observe the following example that implements this scenario: |
using System;
class Program
{
static int Main()
{
double Number1, Number2;
Console.WriteLine("This program allows you to perform a division of two numbers");
try
{
Console.Write("Enter a number: ");
Number1 = double.Parse(Console.ReadLine());
Console.Write("Enter a number: ");
Number2 = double.Parse(Console.ReadLine());
Division(Number1, Number2);
}
catch(DivideByZeroException ex)
{
Console.WriteLine(ex.Message);
}
return 0;
}
static void Division(double a, double b)
{
double Result;
// If an exception occurred,
if( b == 0 ) // then throw a string to the function caller
throw new DivideByZeroException("Division by zero is not allowed");
Result = a / b;
Console.WriteLine("\n{0} / {1} = {2}", a, b, Result);
}
}
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In this program, the Division method receives two values that it is asked to perform a division with. The Division method analyzes the second argument that represents the denominator. If this argument is zero, an exception is found and the Division method throws a DivideByZeroException exception. A method can also be called to perform more than one test to eventually throw more than one exception. Such a method can (and should) be programmed to throw different types of exceptions. |
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