try / catch / finally

// Basic syntax for catching exceptions.
try {
	// Code that may throw an exception
} catch (ExceptionType e) {
	// Code to handle the caught exception
} finally {
	// Code that always runs, regardless of whether an exception occurred
}

using System;

// Basic exception handling.
try {
	int[] arr = new int[3];
	arr[10] = 100; // Index is out of range.
} catch (IndexOutOfRangeException e) {
	Console.WriteLine("Array index out of range: " + e.Message);
}

// Using multiple catch blocks to handle different exception types.
try {
	string input = "abc";
	int number = int.Parse(input); // Throws an exception if conversion fails.
} catch (FormatException e) {
	Console.WriteLine("Format error: " + e.Message);
} catch (OverflowException e) {
	Console.WriteLine("Overflow: " + e.Message);
} catch (Exception e) {
	// Catches all other exceptions (place this last).
	Console.WriteLine("Unexpected error: " + e.Message);
}

// Using finally to ensure cleanup always runs.
System.IO.StreamReader reader = null;
try {
	reader = new System.IO.StreamReader("data.txt");
	Console.WriteLine(reader.ReadToEnd());
} catch (System.IO.FileNotFoundException e) {
	Console.WriteLine("File not found: " + e.Message);
} finally {
	// Close the file regardless of whether an exception occurred.
	reader?.Close();
	Console.WriteLine("finally block executed");
}

// Using a when filter for conditional exception handling.
try {
	throw new Exception("Critical error");
} catch (Exception e) when (e.Message.Contains("Critical")) {
	Console.WriteLine("Critical error detected: " + e.Message);
}

try / catch / finally is the fundamental exception-handling syntax in C#. Always wrap code that may fail at runtime — such as file I/O, network communication, or type conversion — in a try/catch block. Uncaught exceptions will crash your program.

catch blocks are evaluated from top to bottom, so place specific exception types (such as FormatException) before the general Exception catch. If you put the general catch first, the more specific ones will never be reached.

For how to throw exceptions, see 'throw / Custom Exceptions'.