What is the difference between "params" and "array parameter" and when should it be used?

Question

What is the exact difference between these two methods? When to use "params" and when to use array parameters? A reply would be greatly appreciated.

// passing array to a method
class Program
{
    static void printarray(int[] newarray)
    {
        int i,sum=0;
        Console.Write("\n\nYou entered:\t");
        for (i = 0; i < 4; i++)
        {
            Console.Write("{0}\t", newarray[i]);
            sum = sum + newarray[i];
        }
        Console.Write("\n\nAnd sum of all value is:\t{0}", sum);
        Console.ReadLine();
    }
    static void Main(string[] args)
    {
        int[] arr = new int[4];
        int i;
        for (i = 0; i < 4; i++)
        {
            Console.Write("Enter number:\t");
            arr[i] = Convert.ToInt32(Console.ReadLine());
        }
        // passing array as argument
        Program.printarray(arr);
        }
    }
}
//using parameter arrays
public class MyClass
{
public static void UseParams(params int[] list)
{
    for (int i = 0; i < list.Length; i++)
    {
        Console.Write(list[i] + " ");
    }
    Console.WriteLine();
}
static void Main()
{ 
    UseParams(1, 2, 3, 4);
    int[] myIntArray = { 5, 6, 7, 8, 9 };
    UseParams(myIntArray);      
}
}

Answer 1

Using params you can pass zero or more arguments, but with arrays, you have to prodive that argument if it's not optional.For example you can call this method without passing any argument and args will be empty:

public void Foo(params int[] args) { }

Foo(); // no compile-time error, args will be empty

But if you use an array:

public void Foo(int[] args) { }

Foo(); // error: No overload for 'Foo' takes 0 arguments

Otherwise there is not much difference between two. params is just a syntactic sugar.

Answer 2

In addition to Selman's answer, There are some obvious but minor limitations when using params:

According to MS C# reference

No additional parameters are permitted after the params keyword in a method declaration, and only one params keyword is permitted in a method declaration.

This is because the compiler would have hard time identifying which parameter belongs to which. The compiler will also complain if you have normal argument before the params

params parameter must be the last in a formal parameter list.

For example this would not be allowed:

public void Foo(params int[] args,int value) { }