C# Fundamentals – Arrays, Collections, Classes & OOP

Vocabulary flashcards covering key C# terms on arrays, collections, classes, object-oriented principles, file handling, and naming conventions.

Single-dimensional array

A fixed-size linear collection of elements stored in one dimension with index access.

Multi-dimensional array

An array organized in two or more dimensions (e.g., rows × columns) such as 2D or 3D grids.

Collection (C#)

A class that stores, manages and manipulates groups of objects with dynamic sizing.

List

Resizable, ordered collection providing index access and efficient add/remove operations.

Dictionary

Collection that stores value pairs indexed by unique keys for fast lookups.

HashSet

Unordered collection of unique elements using hash codes for quick membership tests.

HashSet.UnionWith()

Adds all elements of another set, keeping only one occurrence of duplicates.

HashSet.IntersectWith()

Retains only elements present in both the current and the specified set.

HashSet.ExceptWith()

Removes from the current set any elements that also exist in another set.

Class

Blueprint that encapsulates data (fields/properties) and behavior (methods) into a single unit.

Property (C#)

Special class member that provides controlled access (get/set) to a private field.

Constructor

Special method called when an object is created to initialize its state; name matches class.

Method

Block of code inside a class that performs actions and can take parameters or return values.

Object

Concrete instance of a class with its own copy of the class’s data.

Encapsulation

OOP principle of bundling data with methods while restricting direct external access.

Abstraction

OOP concept of exposing essential features while hiding complex implementation details.

Inheritance

Mechanism allowing a class (child) to derive attributes and behaviors from another (parent).

Polymorphism

Ability to treat objects of different derived classes as instances of a common base type.

Method overloading

Compile-time polymorphism where multiple methods share a name but differ in parameters.

Method overriding

Run-time polymorphism where a derived class provides its own implementation of a base method.

Virtual method

Base-class method marked to allow overriding by derived classes.

base keyword

Keyword used to call a base-class constructor or access base members from a derived class.

override keyword

Modifier that replaces a virtual/abstract base-class method with a new implementation.

Abstract class

Class that cannot be instantiated and may contain abstract methods requiring overrides.

Interface

Pure contract listing method/property signatures; contains no implementation.

Static class

Class that cannot be instantiated and contains only static members; used for helpers/utility.

Sealed class

Class that cannot be inherited, preventing further extension and sometimes improving performance.

Partial class

Class split across multiple source files to improve organization of large codebases.

Nested class

Class declared inside another class to increase encapsulation and context grouping.

Anonymous class

Compiler-generated temporary type with read-only properties, often used in LINQ projections.

Extension method

Static method in a static class that adds new behavior to an existing type without modifying it.

Static member

Field, property, or method shared by all instances and accessed via the class name.

Access modifier

Keyword that controls visibility of classes and members (public, private, protected, internal).

public

Access modifier allowing visibility from any assembly or class.

private

Access modifier restricting visibility to the containing class only.

protected

Access modifier allowing visibility within the class and its derived classes.

internal

Access modifier limiting visibility to types within the same assembly/project.

Constructor chaining

Technique of calling one constructor from another to reduce code duplication.

File.WriteAllText()

Writes text to a file, overwriting any existing content.

File.AppendAllText()

Adds text to the end of an existing file without deleting current content.

camelCase

Naming style for variables/parameters where the first word is lowercase and subsequent words are capitalized.

PascalCase

Naming style for classes/methods where every word, including the first, is capitalized.

CONSTANTUPPERCASE

Convention of writing constant identifiers in all caps with underscores, e.g., MAX_LIMIT.