MSDN Documentation - .NET API

System Namespace

Provides fundamental classes and base types that define value types, references, and other essential types that are used throughout the .NET Framework and .NET Core. This namespace includes fundamental types, abstract base classes, and interfaces that define commonly used value and reference types, exceptions, converters, and other system-level services.

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Classes

Object
Represents the base type for all types in the .NET Framework and .NET Core.
Class
String
Represents text as a sequence of UTF-16 code units.
Class
Exception
The base class for all exceptions in the .NET Framework and .NET Core.
Class
Console
Provides standard input, output, and error streams for console applications.
Class
DateTime
Represents an instant in time, typically expressed as a date and time of day.
Class
Type
Provides information about the declaration, existence, and attributes of types at run time.
Class

Structs

Int32
Represents a 32-bit signed integer.
Struct
Boolean
Represents a Boolean value (true or false).
Struct
Double
Represents a double-precision 64-bit floating-point number.
Struct

Interfaces

IDisposable
Provides a mechanism for releasing unmanaged resources.
Interface
IEnumerable
Exposes the enumerator, which supports a simple iteration over a collection.
Interface

Enums

ConsoleKey
Specifies the keys on the console and mouse buttons.
Enum

Delegates

Action
Represents a method that takes no arguments and does not return a value.
Delegate
Func
Represents a function that takes no arguments and returns a value.
Delegate