freeCodeCamp/guide/english/csharp/exceptions/index.md

title

title
Exceptions

Exceptions

An exception is an unexpected error that occurs while a program is running, such as an attempt to access a file that does not exist. It will stop the program if not handled.

Example

If we try to read the text of a file that does not exist:

using System.IO;

string content = File.ReadAllText(@"C:\DoesNotExist.txt");

A FileNotFoundException will be raised.

Some other common exceptions:

• IndexOutofRangeException: Attempted to access an array with an invalid index.
• NullReferenceException: Attempted to use an unassigned reference variable.
• DivideByZeroException: Attempted to divide by 0.

Best Practices

Use try/catch/finally Blocks

try
{
   var client = new WebClient();
   var resultData = client.DownloadString("http://github.com");
}
catch (Exception ex)
{
   //code for handling exceptions
}
finally
{
   //this code is always executed, does not matter if an exception is thrown or not
}         

Handle Possible Exceptions With Conditions

Instead of

try
{
   conn.Close();
}
catch (Exception ex)
{
   //code for handling exceptions.
}

Try this

if (conn.State != ConnectionState.Closed)
{
    conn.Close();
}