Type checking and conversion are essential operations in C#'s object-oriented programming model.
The is and as keywords provide elegant solutions for safely working with types at runtime. Understanding when and how to use each can significantly improve your code's robustness and readability.
is
as
The is operator evaluates whether an object is compatible with a given type, returning a boolean result.
object value = "Hello, World!"; // Check if value is a string if (value is string) { Console.WriteLine("value is a string"); }
// Type checking with declaration if (value is string message) { // message is now a string variable containing the value Console.WriteLine($"Length: {message.Length}"); }
// Check type and condition in one step if (value is string { Length: > 5 } longString) { Console.WriteLine($"Long string found: {longString}"); }
The as operator attempts to cast an object to a specified reference type, returning null if the cast fails rather than throwing an exception.
null
object value = "Hello, World!"; // Try to cast to string string message = value as string; // Check if cast was successful if (message != null) { Console.WriteLine($"Successful cast: {message}"); }
Understanding these operators helps you write more elegant, safe code when working with polymorphic types in C#.
When working with URLs in C#, encoding is essential to ensure that special characters (like spaces, ?, &, and =) don’t break the URL structure. The recommended way to encode a string for a URL is by using Uri.EscapeDataString(), which converts unsafe characters into their percent-encoded equivalents.
string rawText = "hello world!"; string encodedText = Uri.EscapeDataString(rawText); Console.WriteLine(encodedText); // Output: hello%20world%21
This method encodes spaces as %20, making it ideal for query parameters.
For ASP.NET applications, you can also use HttpUtility.UrlEncode() (from System.Web), which encodes spaces as +:
using System.Web; string encodedText = HttpUtility.UrlEncode("hello world!"); Console.WriteLine(encodedText); // Output: hello+world%21
For .NET Core and later, Uri.EscapeDataString() is the preferred choice.
In C#, you can format an integer with commas (thousands separator) using ToString with a format specifier.
int number = 1234567; string formattedNumber = number.ToString("N0"); // "1,234,567" Console.WriteLine(formattedNumber);
Explanation:
"N0": The "N" format specifier stands for Number, and "0" means no decimal places. The output depends on the culture settings, so in regions where , is the decimal separator, you might get 1.234.567.
Alternative:
You can also specify culture explicitly if you need a specific format:
using System.Globalization; int number = 1234567; string formattedNumber = number.ToString("N0", CultureInfo.InvariantCulture); Console.WriteLine(formattedNumber); // "1,234,567"
Reading a file line by line is useful when handling large files without loading everything into memory at once.
✅ Best Practice: Use File.ReadLines() which is more memory efficient.
Example
foreach (string line in File.ReadLines("file.txt")) { Console.WriteLine(line); }
Why use ReadLines()?
Reads one line at a time, reducing overall memory usage. Ideal for large files (e.g., logs, CSVs).
Alternative: Use StreamReader (More Control)
For scenarios where you need custom processing while reading the contents of the file:
using (StreamReader reader = new StreamReader("file.txt")) { string? line; while ((line = reader.ReadLine()) != null) { Console.WriteLine(line); } }
Why use StreamReader?
Lets you handle exceptions, encoding, and buffering. Supports custom processing (e.g., search for a keyword while reading).
When to Use ReadAllLines()? If you need all lines at once, use:
string[] lines = File.ReadAllLines("file.txt");
Caution: Loads the entire file into memory—avoid for large files!
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