Types

In C# all variables have a type, which determines what kind of data they store. There are two types of type, value and reference.

Value Types

Value types store a value.

Here is the list of value types in C#:

C# type keyword	.NET type
bool	System.Boolean
byte	System.Byte
sbyte	System.SByte
char	System.Char
decimal	System.Decimal
double	System.Double
float	System.Single
int	System.Int32
uint	System.UInt32
nint	System.IntPtr
nuint	System.UIntPtr
long	System.Int64
ulong	System.UInt64
short	System.Int16
ushort	System.UInt16

Reference Types

Reference types store a reference to something (kind of like a pointer in C) Notably, all objects (instances of a class) are reference types!

Here is the list of reference types in C#:

C# type keyword	.NET type
object	System.Object
string	System.String
delegate	System.Delegate
dynamic	System.Object

The “var” keyword

The var keyword allows C# to perform something called type inference, where the runtime decides what type something is based on what value is assigned to it.

For example:

var a = 1;        // a becomes an integer
var b = 1.123;    // b becomes a float
var c = "Hello!"; // c becomes a string

Note that this can only be used when the compiler knows what the type is upon compilation!

The following is not legal:

int add(var a, var b) {
	return a+b;
}