Async/Await and Error Handling

Modern applications must handle I/O operations (network calls, file access, database queries) without blocking. C# provides a first-class async/await model built on the Task type. This lesson also covers structured error handling with exceptions.

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Error Handling with Exceptions

try/catch/finally

try
{
    string content = File.ReadAllText("data.txt");
    int number = int.Parse(content);
    Console.WriteLine($"Result: {number}");
}
catch (FileNotFoundException ex)
{
    Console.WriteLine($"File not found: {ex.FileName}");
}
catch (FormatException ex)
{
    Console.WriteLine($"Invalid format: {ex.Message}");
}
catch (Exception ex)
{
    // Catch-all for unexpected exceptions
    Console.WriteLine($"Unexpected error: {ex.Message}");
}
finally
{
    // Always runs — cleanup code
    Console.WriteLine("Cleanup complete");
}

Exception Hierarchy

Exception	When
Exception	Base class for all exceptions
SystemException	Base for runtime exceptions
ArgumentException	Invalid argument
ArgumentNullException	Null argument
InvalidOperationException	Operation not valid for current state
NullReferenceException	Accessing a member on null
IndexOutOfRangeException	Array index out of bounds
IOException	I/O operation failed
HttpRequestException	HTTP request failed
TaskCanceledException	Task was cancelled

Throwing Exceptions