C# week7_2

09/03/2010

Exception

• compile time error
  
• run time error
  

   
   

  exception handling: how to handle exception
  

  • try
    
  • catch
    
  • finally
    
  • throw
    

     
     

  Divide by Zero exception
  

  1/0 = ∞
  →System error
  

   
   

  public static void Main()
  

  {
  

  Console.WriteLine("Please enter a number.");
  

  string num = Console.ReadLine();
  

  try
  

  {
  

  int i = int.Parse(num); // If user put in alphabet, it won't work. →Guard for future
  

  int j = 5 / i; //If user put in 0, it won't work. →Guard for future
  

  Console.WriteLine("Result" + j);
  

  }
  

  catch
  

  {
  

  Console.WriteLine("Don't allow to put in 0.");
  

  }
  

  }
  

   
   

  Real industry
  

   
   

  System
  

  |
  

  Exception (class) : Using inheritance
  

  ___|___________________
  

  | | | | ………
  

  Divide X y z
  

  byZero
  

   
   

  try
  

  {
  

  int j=5/0
  

  }
  

  catch(DevidebyZero s)
  

  { ---------------- ---
  

  classname variable name
  

  }
  

  catch(Exception e)
  

  {
  

  }
  

  • In case of divide by zero, exception is caught by catch divide by class.
    
  • In other case, exception is caught by catch exception class.
    

   
   

  Pros.
  

  Program don't stop.
  

  It will be shown meaningful message.
  

   
   

----------------1	○	○
----------------2	○	○

try

{

----------------3	○	○
----------------4	○	×

}

catch

{

----------------5		○
----------------6		○

}

finally

{

---------------7	○	○
---------------8	○	○

}

---------------9

○

○

 
 

*Finally block is always executed.

 
 

Option

1. try & catch
   
2. try & finally
   
3. try & catch & finally
   

 
 

throw

try

{

throw new Exception(); //using to throw an exception programmatically.

}

 
 

 
 

static memory: int i=5;

dynamic memory: file