C# Data Types

1. Introduction

In C#, every variable has a type, which determines the size of the variable's memory, the range of values that can be stored within that memory, and the set of operations that can be applied to the variable.

Category Data Type Size/Range Description
Numeric (Value Types) byte 1 byte, 0 to 255 Unsigned 8-bit integer
sbyte 1 byte, -128 to 127 Signed 8-bit integer
short 2 bytes, -32,768 to 32,767 Signed 16-bit integer
ushort 2 bytes, 0 to 65,535 Unsigned 16-bit integer
int 4 bytes, -2^31 to 2^31-1 Signed 32-bit integer
uint 4 bytes, 0 to 2^32-1 Unsigned 32-bit integer
long 8 bytes, -2^63 to 2^63-1 Signed 64-bit integer
ulong 8 bytes, 0 to 2^64-1 Unsigned 64-bit integer
float 4 bytes Single-precision floating point
double 8 bytes Double-precision floating point
decimal 16 bytes Precise decimal for financial calculations
Others char 2 bytes Single Unicode character
bool 1 bytes Boolean value (true/false)
Reference (Reference Types) object NA Base class for all other types
string NA Sequence of characters
class NA User-defined data type
interface NA Contract that classes or structs can implement
delegate NA Reference to methods with a specific signature
Special nullable <T> NA Allows null values for value types
dynamic NA Type determined at runtime
pointer (unsafe) NA Directly addresses memory locations
Immutable record NA Immutable reference type that represents a data structure

2. Value Types

Value types directly store data. When you assign one value type to another, a copy of the data is made. The actual data is stored in the stack or in the location directly associated with the variable.

2.1. Basic Types Numeric Types: Other Value Types: 2.2. Struct

User-defined value types. For example: 

        
            struct Point
{
    public int x, y;
}
2.3. Enum

Enumerations (or enums) are named integer constants. For example: 

        
            enum Days { Sun, Mon, Tue, Wed, Thu, Fri, Sat };

3. Reference Types

The variable doesn't directly store the data. Instead, it stores a reference (or a pointer) to the memory location where the actual data is kept, which is typically in the heap. This is what the statement "reference types store a reference to the memory location" means.

3.1. Object

The base class for all data types in C#. Can store any type of value.

3.2. String

Represents a sequence of characters. For example: 

        
            string name = "John";
3.3. Classes, Interfaces & Delegates

User-defined data structures. Classes encapsulate data for the object and methods to manipulate that data.

4. Nullable Types

C# provides a special data types, the nullable types, to which you can assign normal range of values as well as null values. For example: 

        
            int? num = null;

Dynamic Types

Declared with the dynamic keyword. The type of variable declared is decided by the compiler at runtime. 

        
            dynamic val = 100;

6. Pointer Types

Allows storing the memory address. Not common in C# due to safety concerns and is mostly used in unsafe programming.

Conclusion

Understanding data types is fundamental in C#. They determine the kind of data a variable can hold and the operations that can be performed on them. Familiarize yourself with the above types to make the best out of C# programming.