What is the difference between String and string and var?

Question

I have this use case:

using System;
namespace ConsoleApplication11
{
  using System.Collections.ObjectModel;

  public class Program
  {
    static void Main(string[] args)
    {
      var test2 = "Name";
      string test1 = "Name";
      String test3 = "Name";

     Console.WriteLine(test1 + test2 + test3 + "NameNotDefined");
   }
 }
}

What will do the compiler:

in this line Console.WriteLine(test1 + test2 + test3 + "Alugili");?
with the last one "NameNotDefined"?

Did the compiler call ToString() to each of them and than apply the + Operator?

Any body can please explain to me the difference between the var and String and string and "" and how the complier will interact with them?

`string` is an alias of `System.String` `var` is temporary varaible — Praveen, Sep 11 '13 at 13:04
They are all the same (var is changed to string based on semantics by the compiler) — Kevin DiTraglia, Sep 11 '13 at 13:05
@user1671639 `var` is not temporary... it's implicitly typed local variable. — MarcinJuraszek, Sep 11 '13 at 13:05
Another topic involved http://stackoverflow.com/questions/41479/use-of-var-keyword-in-c-sharp — Sergey Berezovskiy, Sep 11 '13 at 13:05
I have a feeling ppl here closing a questions before even read it!!!!!!!!!!!!! — Bassam Alugili, Sep 11 '13 at 13:08
@BassamAlugili Is it too much to ask to read the documentation? Everyone did read your question and closed it appropriately — tnw, Sep 11 '13 at 13:10
Your question is void as you haven't understood how the variables are defined to begin with, you basically have `string + string + string` if it will help you understand — Sayse, Sep 11 '13 at 13:10
@MarcinJuraszek `var` keyword is used to refer vary datatype within a local scope, is my understanding. Please correct me if I was wrong — Praveen, Sep 11 '13 at 13:15

score 1 · Answer 1 · answered Sep 11 '13 at 13:05

1

All three compile identically in C#. The "var" keyword is used to infer the type at compile-time, and the compiler infers that you're using a string (which is the same thing as String).

answered Sep 11 '13 at 13:05

Dave Markle

88,065
20
140
165

score 1 · Answer 2 · edited Sep 11 '13 at 13:17

1

string is an alias for System.String, both of them compile to the same code, so at execution time there is no difference.

The + is used for string concatenation, so when you write test1 + test2 + test3 + "Alugili" it concatenates all of the strings and form one string. In .net string's are immutable i.e. strings cannot be altered. When you alter a string, you are actually creating a new string.

About var MSDN says this :

Beginning in Visual C# 3.0, variables that are declared at method scope can have an implicit type var. An implicitly typed local variable is strongly typed just as if you had declared the type yourself, but the compiler determines the type. The following two declarations of i are functionally equivalent:

edited Sep 11 '13 at 13:17

Sayse

38,955
14
69
129

answered Sep 11 '13 at 13:05

Bibhu

3,943
4
29
61

So in the last one "Alugili" a new object of type string will be created and injected to code you mean that? – Bassam Alugili Sep 11 '13 at 13:15
1

@Bassam Alugili - Yes, for more info check out this MSDN link http://msdn.microsoft.com/en-us/library/ms228362%28v=vs.90%29.aspx – Bibhu Sep 11 '13 at 13:24

What is the difference between String and string and var?

2 Answers2