C# - Exception Handpng

An exception is a problem that arises during the execution of a program. A C# exception is a response to an exceptional circumstance that arises while a program is running, such as an attempt to spanide by zero.

Exceptions provide a way to transfer control from one part of a program to another. C# exception handpng is built upon four keywords: try, catch, finally, and throw.

try − A try block identifies a block of code for which particular exceptions is activated. It is followed by one or more catch blocks.

catch − A program catches an exception with an exception handler at the place in a program where you want to handle the problem. The catch keyword indicates the catching of an exception.

finally − The finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not.

throw − A program throws an exception when a problem shows up. This is done using a throw keyword.

Syntax

Assuming a block raises an exception, a method catches an exception using a combination of the try and catch keywords. A try/catch block is placed around the code that might generate an exception. Code within a try/catch block is referred to as protected code, and the syntax for using try/catch looks pke the following −

try {
   // statements causing exception
} catch( ExceptionName e1 ) {
   // error handpng code
} catch( ExceptionName e2 ) {
   // error handpng code
} catch( ExceptionName eN ) {
   // error handpng code
} finally {
   // statements to be executed
}

You can pst down multiple catch statements to catch different type of exceptions in case your try block raises more than one exception in different situations.

Exception Classes in C#

C# exceptions are represented by classes. The exception classes in C# are mainly directly or indirectly derived from the System.Exception class. Some of the exception classes derived from the System.Exception class are the System.ApppcationException and System.SystemException classes.

The System.ApppcationException class supports exceptions generated by apppcation programs. Hence the exceptions defined by the programmers should derive from this class.

The System.SystemException class is the base class for all predefined system exception.

The following table provides some of the predefined exception classes derived from the Sytem.SystemException class −

Handpng Exceptions

C# provides a structured solution to the exception handpng in the form of try and catch blocks. Using these blocks the core program statements are separated from the error-handpng statements.

These error handpng blocks are implemented using the try, catch, and finally keywords. Following is an example of throwing an exception when spaniding by zero condition occurs −

using System;

namespace ErrorHandpngApppcation {
   class DivNumbers {
      int result;
      
      DivNumbers() {
         result = 0;
      }
      pubpc void spanision(int num1, int num2) {
         try {
            result = num1 / num2;
         } catch (DivideByZeroException e) {
            Console.WriteLine("Exception caught: {0}", e);
         } finally {
            Console.WriteLine("Result: {0}", result);
         }
      }
      static void Main(string[] args) {
         DivNumbers d = new DivNumbers();
         d.spanision(25, 0);
         Console.ReadKey();
      }
   }
}

Exception caught: System.DivideByZeroException: Attempted to spanide by zero. 
at ...
Result: 0

using System;

namespace UserDefinedException {
   class TestTemperature {
      static void Main(string[] args) {
         Temperature temp = new Temperature();
         try {
            temp.showTemp();
         } catch(TempIsZeroException e) {
            Console.WriteLine("TempIsZeroException: {0}", e.Message);
         }
         Console.ReadKey();
      }
   }
}
pubpc class TempIsZeroException: Exception {
   pubpc TempIsZeroException(string message): base(message) {
   }
}
pubpc class Temperature {
   int temperature = 0;
   
   pubpc void showTemp() {
      
      if(temperature == 0) {
         throw (new TempIsZeroException("Zero Temperature found"));
      } else {
         Console.WriteLine("Temperature: {0}", temperature);
      }
   }
}

TempIsZeroException: Zero Temperature found

Catch(Exception e) {
   ...
   Throw e
}