11.3 Using .NET built-in Libraries

Absolutely! Let’s go through using .NET built-in libraries in C# — powerful collections of classes and functions that simplify common programming tasks.

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📌 1. System.IO – Input/Output

• Provides classes for working with files, directories, and streams

• Commonly used classes:

  • File → high-level file operations (ReadAllText, WriteAllText)

  • FileInfo → detailed file information and manipulation

  • Directory → create, delete, and enumerate directories

  • StreamReader / StreamWriter → reading/writing text files

  • FileStream → low-level byte-based file access

Example: Reading a File

using System.IO;
 
string content = File.ReadAllText("example.txt");
Console.WriteLine(content);

Example: Writing a File

File.WriteAllText("output.txt", "Hello, World!");

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📌 2. System.Text – Text Processing

• Provides classes for encoding, string building, and regular expressions

• Commonly used classes:

  • StringBuilder → efficient string concatenation

  • Encoding → convert strings to bytes and vice versa

  • Regex → regular expressions for pattern matching

Example: Using StringBuilder

using System.Text;
 
StringBuilder sb = new StringBuilder();
sb.Append("Hello");
sb.Append(" ");
sb.Append("World!");
Console.WriteLine(sb.ToString()); // Hello World!

Example: Using Encoding

byte[] bytes = Encoding.UTF8.GetBytes("Hello");
string text = Encoding.UTF8.GetString(bytes);
Console.WriteLine(text);

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📌 3. System.Collections – Collections

• Provides basic collection classes (non-generic):

  • ArrayList → dynamically sized array

  • Hashtable → key-value storage

  • Queue, Stack → FIFO and LIFO collections

• For type-safe collections, prefer System.Collections.Generic

Example: Using ArrayList

using System.Collections;
 
ArrayList list = new ArrayList();
list.Add(1);
list.Add("Hello");
foreach (var item in list)
{
    Console.WriteLine(item);
}

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📌 4. Why Use Built-in Libraries

Library	Purpose
System.IO	File, directory, and stream operations
System.Text	Efficient string handling, encoding, regex
System.Collections	Basic collections, queues, stacks, hashtables

• Speeds up development

• Provides tested, optimized functionality

• Reduces need for manual implementations

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📌 5. Best Practices

1. Prefer generic collections (List<T>, Dictionary<K,V>) over ArrayList and Hashtable

2. Use StringBuilder when concatenating strings in loops

3. Always dispose streams using using blocks to release resources

4. Use System.Text.RegularExpressions.Regex for complex pattern matching

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📌 6. Summary Table

Namespace	Common Classes	Example Use Case
System.IO	File, StreamReader, FileStream	Reading/writing files
System.Text	StringBuilder, Encoding, Regex	String manipulation, encoding, pattern matching
System.Collections	ArrayList, Hashtable, Queue, Stack	Simple non-generic collections

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✅ Tip:

• Built-in libraries are the backbone of C# development — learn them well.

• For modern applications, prefer generic collections from System.Collections.Generic for type safety and performance.

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I can also make a diagram showing System.IO for file operations, System.Text for string/encoding, and System.Collections for collections — visually connecting their roles.

Do you want me to create that diagram?