Csharp/CSharp Tutorial/Language Basics/Try Catch

A try, catch, and finally block without Exception class declaration

using System;
class MainClass
{
  public static void Main()
  {
    try
    {
      int zero = 0;
      Console.WriteLine("In try block: attempting division by zero");
      int myInt = 1 / zero;
      Console.WriteLine("You never see this message!");
    }
    catch
    {
      Console.WriteLine("In catch block: an exception was thrown");
    }
    finally
    {
      Console.WriteLine("In finally block: do any cleaning up here");
    }
  }
}

In try block: attempting division by zero
In catch block: an exception was thrown
In finally block: do any cleaning up here

Catch exception with wrong type inside a function

using System;
class MainClass
{
    
    static void AFunction()
    {
        
        try {
            int Zero = 0;
            int j = 22 / Zero;
        } catch (ArgumentOutOfRangeException e) // this exception doesn"t match
        {
            Console.WriteLine("OutOfRangeException: {0}", e);
        }
        Console.WriteLine("In AFunction()");
    }
    public static void Main()
    {
        try
        {
            AFunction();
        }
        // this exception doesn"t match
        catch (ArgumentException e)
        {
            Console.WriteLine("ArgumentException {0}", e);
        }catch(Exception ee){
            Console.WriteLine("Exception {0}", ee);
        }
    }
}

Exception System.DivideByZeroException: Attempted to divide by zero.
   at MainClass.AFunction()
   at MainClass.Main()

Catch statement without exception variable

using System;
class MainClass
{
   static void Main()
   {
      int x = 10, y = 0;
      
      try { 
      
         x = x/y; 
      
      }catch (System.IndexOutOfRangeException) { 
      
         Console.WriteLine("catch clause"); 
      
      } finally { 
      
         Console.WriteLine("finally clause"); 
      
      }
   }
}

Unhandled Exception: System.DivideByZeroException: Attempted to divide by zero.
   at MainClass.Main()
finally clause

Catch System.NullReferenceException

using System;
class MainClass
{
   static void Main()
   {
      try { 
      
         string str = null;
         str.ToUpper();
      
      }catch (System.NullReferenceException) { 
      
         Console.WriteLine("catch clause"); 
      
      } finally { 
      
         Console.WriteLine("finally clause"); 
      
      }
   }
}

catch clause
finally clause

Exception Handling Fundamentals

C# exception handling is managed via four keywords: try, catch, throw, and finally.

try {
        // block of code to monitor for errors
    }
    catch (ExcepType1 exOb) {
        // handler for ExcepType1 
    }
    catch (ExcepType2 exOb) {
        // handler for ExcepType2 
    }
    .
    .
    finally{
    
    }

If no exception is thrown by a try block, no catch statements will be executed and program control resumes after the catch statement.

Exception handling with trying and catching

using System;
class MainClass{
    
    
    public static void Main(){
        Console.WriteLine("Before catch");
        int Zero = 0;
        try {
            int j = 22 / Zero;
        } catch (Exception e) {
            Console.WriteLine("Exception " + e.Message);
        }
        
        Console.WriteLine("After catch");
    }
}

Before catch
Exception Attempted to divide by zero.
After catch

Handle error gracefully and continue.

using System; 
 
class MainClass { 
  public static void Main() { 
      try { 
        int j= 0;
        int i = 5/j;
      } 
      catch (DivideByZeroException) { 
        // catch the exception 
        Console.WriteLine("Can"t divide by Zero!"); 
      } 
  } 
}

Can"t divide by Zero!

How to handle a specific exception

using System;
class MainClass{
  public static void Main() {
    try {
      int zero = 0;
      Console.WriteLine("In try block: attempting division by zero");
      int myInt = 1 / zero;
    } catch (DivideByZeroException myException) {
      Console.WriteLine("Message = " + myException.Message);
      Console.WriteLine("StackTrace = " + myException.StackTrace);
    }
  }
}

In try block: attempting division by zero
Message = Attempted to divide by zero.
StackTrace =    at MainClass.Main()

Let the C# runtime system handle the error.

using System; 
 
class MainClass { 
  public static void Main() { 
    int[] nums = new int[4]; 
 
    Console.WriteLine("Before exception is generated."); 
 
    // Generate an index out-of-bounds exception. 
    for(int i=0; i < 10; i++) { 
      nums[i] = i; 
      Console.WriteLine("nums[{0}]: {1}", i, nums[i]); 
    } 
 
  } 
}

Before exception is generated.
nums[0]: 0
nums[1]: 1
nums[2]: 2
nums[3]: 3
Unhandled Exception: System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at MainClass.Main()

Use a nested try block.

using System; 
 
class MainClass { 
  public static void Main() { 
    int[] numer = { 4, 8, 16, 32, 64, 128, 256, 512 }; 
    int d = 0;
 
    try { // outer try 
      for(int i=0; i < 10; i++) { 
        try { // nested try 
          Console.WriteLine(numer[i] + " / " + 
                             numer[i] + " is " + 
                             numer[i]/d); 
        } 
        catch (DivideByZeroException) { 
          // catch the exception 
          Console.WriteLine("Can"t divide by Zero!"); 
        } 
      } 
    }  
    catch (IndexOutOfRangeException) { 
      // catch the exception 
      Console.WriteLine("No matching element found."); 
      Console.WriteLine("Fatal error -- program terminated."); 
    } 
  } 
}

Can"t divide by Zero!
Can"t divide by Zero!
Can"t divide by Zero!
Can"t divide by Zero!
Can"t divide by Zero!
Can"t divide by Zero!
Can"t divide by Zero!
Can"t divide by Zero!
No matching element found.
Fatal error -- program terminated.

Use multiple catch statements.

using System; 
 
class MainClass { 
  public static void Main() { 
    int[] numer = { 4, 8, 16}; 
    int j=0;
    
    for(int i=0; i < 10; i++) { 
      try { 
        Console.WriteLine(numer[i] + " / " + 
                           numer[i] + " is " + 
                           numer[i]/j); 
      } 
      catch (DivideByZeroException) { 
        // catch the exception 
        Console.WriteLine("Can"t divide by Zero!"); 
      } 
      catch (IndexOutOfRangeException) { 
        // catch the exception 
        Console.WriteLine("No matching element found."); 
      } 
    } 
  } 
}

Can"t divide by Zero!
Can"t divide by Zero!
Can"t divide by Zero!
No matching element found.
No matching element found.
No matching element found.
No matching element found.
No matching element found.
No matching element found.
No matching element found.

Use the "catch all" catch statement.

using System; 
 
class MainClass { 
  public static void Main() { 
    int[] numer = { 4, 8}; 
    int d = 0;
    
    for(int i=0; i < 10; i++) { 
      try { 
        Console.WriteLine(numer[i] + " / " + 
                           numer[i] + " is " + 
                           numer[i]/d); 
      } 
      catch { 
        Console.WriteLine("Some exception occurred."); 
      } 
    } 
  } 
}

Some exception occurred.
Some exception occurred.
Some exception occurred.
Some exception occurred.
Some exception occurred.
Some exception occurred.
Some exception occurred.
Some exception occurred.
Some exception occurred.
Some exception occurred.