var keyword indicates that the variable type is not declared during definition, but can be
decided by the compiler.
//Common variable definition
int i=3; //type is int
string s="csharp"; //type is string
var i=3; //type is unknown, but compiler can infer its type is int
keyword defined variable must be initialized during definition.
The type of the variable can then be decided based on the value. After definition,
the variable type can not be changed.
var s; //error
var s = "csharp";
s = 3; //error
defined variable must be a local variable.