What is wrong with this code ?

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SoloLearn
{
class Program
{
static void Main(string[] args)
{
string spaced = "ab c d e fgh i j kl mn opqr stuvwxyz";
char[] unspaced = spaced.ToCharArray();
string empty = null;
foreach (char s in unspaced)
if (char.IsLetter(s))
{
empty += s;
}
}
Console.Write(empty);
}
}

Answer 1

Console.Write(empty) ; is out of main method.
Write inside main, put before brace, after write.