What is the difference between String and string in C#?

Question

Example (note the case):

string s = \"Hello world!\";
String s = \"Hello world!\";

What are

Answer 1

string is a keyword, and you can't use string as an identifier.

String is not a keyword, and you can use it as an identifier:

Example

string String = "I am a string";

The keyword string is an alias for System.String aside from the keyword issue, the two are exactly equivalent.

 typeof(string) == typeof(String) == typeof(System.String)