Data and Collections

Arrays, collections, generics, and LINQ for effective data handling and querying in C#.

Data and Collections

In C# applications, data is managed through arrays, lists, and dictionaries. Generics ensure type safety, while LINQ makes it easy to query and transform data.

This section also introduces file input/output operations and using Entity Framework Core for database queries.

TL;DR

Collections: List<T>, Dictionary.
LINQ: Where, Select, GroupBy.
File operations: StreamReader, StreamWriter.

Arrays in C#

19 February 2026 • Data and Collections

Learn arrays in C#, including declaration, indexing, looping through elements, and common array operations with examples.

Arrays C#

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Collections in C#: List, Dictionary, Queue, Stack

19 February 2026 • Data and Collections

Learn C# collections like List, Dictionary, Queue, and Stack to store and manage data efficiently with practical examples.

C# C# Collections Dictionaries Lists Queues Stacks

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Generics in C# (List<T>, Dictionary<TKey,TValue>)

24 February 2026 • Data and Collections

Learn generics in C#, including List<T> and Dictionary<TKey,TValue>, to write type-safe and reusable code with examples.

C# C# Generics Dictionaries Lists

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LINQ Basics in C# (Where, Select, OrderBy)

26 February 2026 • Data and Collections

Learn LINQ basics in C# using Where, Select, and OrderBy to query, filter, and sort collections with practical examples.

C# LINQ Basics

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In C#, use a for loop instead of foreach when you need the index or when you need to modify the collection safely.


// foreach: index bilgisi yok
foreach (var item in items)
{
    Console.WriteLine(item);
}

// for: index gerektiğinde
for (int i = 0; i < items.Count; i++)
{
    Console.WriteLine($"{i}: {items[i]}");
}

// for: eleman silme gibi durumlarda daha güvenli
for (int i = items.Count - 1; i >= 0; i--)
{
    items.RemoveAt(i);
}

In C#, use Guid.Empty instead of new Guid() when you want an empty GUID. It makes the code clearer.


// Less clear
Guid id1 = new Guid();

// Clear and recommended
Guid id2 = Guid.Empty;

Console.WriteLine(id1 == id2); // True

Using DateTime.UtcNow instead of DateTime.Now prevents timezone-related bugs in distributed systems.


// Local time (depends on server timezone)
DateTime localTime = DateTime.Now;

// Universal time (recommended)
DateTime utcTime = DateTime.UtcNow;

Console.WriteLine(localTime);
Console.WriteLine(utcTime);

In C#, var should be used when the type is clearly understood from the right side. It improves readability without hiding information.


// Clear and readable: type is obvious
var numbers = new List<int>();
var name = "Alice";
var total = numbers.Count;

// Not recommended: type is not obvious
var result = GetData();

// Recommended alternative
List<User> users = GetUsers();

In C#, use string.IsNullOrWhiteSpace() to check text values instead of checking only for null or empty strings.


// Risky checks
if (text == null || text == "")
{
    Console.WriteLine("Invalid text");
}

// Safe and recommended check
if (string.IsNullOrWhiteSpace(text))
{
    Console.WriteLine("Invalid text");
}