C# Programming/Keywords/var

The var keyword can be used in place of a type when declaring a variable to allow the compiler to infer the type of the variable. This feature can be used to shorten variable declarations, especially when instantiating generic types, and is even necessary with LINQ expressions (since queries may generate very complex types).

The following:

int num = 123;
string str = "asdf";
Dictionary<int, string> dict = new Dictionary<int, string>();

is equivalent to:

var num = 123;
var str = "asdf";
var dict = new Dictionary<int, string>();

var does not create a "variant" type; the type is simply inferred by the compiler. In situations where the type cannot be inferred, the compiler generates an error:

var str; // no assignment, can't infer type

void Function(var arg1, var arg2) // can't infer type

C# Keywords
abstract as base bool break
byte case catch char checked
class const continue decimal default
delegate do double else enum
event explicit extern false finally
fixed float for foreach goto
if implicit in int interface
internal is lock long namespace
new null object operator out
override params private protected public
readonly ref return sbyte sealed
short sizeof stackalloc static string
struct switch this throw true
try typeof uint ulong unchecked
unsafe ushort using var virtual
void volatile while
Special C# Identifiers (Contextual Keywords)
add alias async await dynamic
get global nameof partial remove
set value when where yield
Contextual Keywords (Used in Queries)
ascending by descending equals from
group in into join let
on orderby select where

Note: Var is not a keyword