An output parameter is used for output parameter passing, an output parameter is similar to a reference parameter except that the initial value of the caller-provided argument is unimportant. an output parameter is declared with the out modifier.

Static and instance methods

• A static method does not operate on a specific instance and can only directly access static members.
• An instance method operaten a specific instance and can access both static and instance members

A parameter array

• Permits a variable number of arguments to be passed to a method. A parameter array is declared with the params modifier. Only the last parameter of a method can be a parameter array, and the type of a parameter array must be a single-dimensional array type. The Write and WriteLine methods of the System.Console class are good examples of parameter array usage. They are declared as follows.

  public class Console
  {
  public static void Write(string fmt, params object[] args) {...}

  public static void WriteLine(string fmt, params object[] args) {...}

  ...
  }

  Within a method that uses a parameter array, the parameter array behaves exactly like a regular parameter of an array type. However, in an invocation of a method with a parameter array, it is possible to pass either a single argument of the parameter array type or any number of arguments of the element type of the parameter array. In the latter case, an array instance is automatically created and initialized with the given arguments. This example

  Console.WriteLine("x={0} y={1} z={2}", x, y, z);

  is equivalent to writing the following.

  string s = "x={0} y={1} z={2}";
  object[] args = new object[3];
  args[0] = x;
  args[1] = y;
  args[2] = z;
  Console.WriteLine(s, args);

…