Lets take a look at what the params keyword does.

It mainly gives you the ability to create functions that take a variable number of arguments - often called “variadic” or “variable arity” functions. This is not a really new feature only provided by C# you can also find it in C and C++, in the form of the “…” syntax, and Java uses that syntax as well. (e.g. Exception{} catch(…))

I’d like to show how useful the usage in C# can be:

public int Sum(params int[] list)
{
  int res = 0;
  foreach (int i in list)
    res += i;
  return res;
}

As you can see, the params keyword is used as an argument list for a number of typed vars.

You can call that small function with zero or more arguments.

int result = Sum(5);
result = Sum(5,4,3,4);
result  = Sum(new int[] { 3,4,4,2,11 });
result  = Sum();

This would report an error because the arguments are invalid:

int result = Sum(1,2,3 new int[] { 4,5,6 });

Even though you can pass in lists/array for the params, you can’t mix it up with regular values at all.