Question

That can be silly question but I really don’t know the reason.

    // i is compiled as an int
    var i = 5;

    // s is compiled as a string
    var s = "Hello";

    // a is compiled as int[]
    var a = new[] { 0, 1, 2 };

    // expr is compiled as IEnumerable<Customer>
    // or perhaps IQueryable<Customer>
    var expr =
        from c in customers
        where c.City == "London"
        select c;

    // anon is compiled as an anonymous type
    var anon = new { Name = "Terry", Age = 34 };

    // list is compiled as List<int>                             
    var list = new List<int>();

If so, why C# needs integral types like int, string, int[], List<> ? If we can do that only with var keywords, why are there integral types?

Another way,

What is the difference between these ?

var s = "Hello";
string s = "Hello";

Answer 1

in no particular order…

• var is only a compiler construct; even var i = 4; is typed as int
• C# hasn’t always had var, and you can’t remove keywords without utterly breaking existing code.
• you can only use var in method variables – not fields, parameters, return types etc.
• most people are happy to type int in place of var! Especially when the type matters and there are bytes, floats, enums, decimals etc that all work with the literal 0; i.e. short x = 0; int y = 0; long z = 0; – why change only int to var there?
• you can’t use var to specify a generic type parameter (<T>) or in a typeof
• you can’t use var.TryParse in place of int.TryParse