The example you give is false. Valid parentheses are not just defind by starting with an open paren ( and ending with a closed paren ). They have to be matched. Is )( valid?`

Convert is in the System namespace, so you have to define using System; at the top of your solution. Note that you can also use int.Parse(string).

I'm playing around with digits ;) but I always seem to have an error with the line: 'number = Convert.ToInt32(str);', even though other katas and pages show that this is a correct line for c# code to convert text to integer. I believe its the last error I have but I can't seem to solve it. Could anyone help? Thanks! (Error: The name 'Convert' does not exist in the current context)

array2.Length is undefined and JS would never complain you about that, you should use array2.length

An advice: Don't start your programmming career with JS.