where are my mistakes?

Question

int[] arr = new int[] { 2, 4, 5, 8, 9, 7, 6, 3 };
Array.Sort(arr);
foreach (int i in arr)
{
Console.WriteLine(arr[i]);
}

string S1 = "keep";
string S2 = "Going";

Console.WriteLine(string.Concat(S1, S2));

Console.WriteLine(string.Equals(S1, S2));

Console.WriteLine(DateTime.DaysInMonth(2017, 2));

Console.ReadLine();

Answer 1

int[] arr = { 2, 4, 5, 8, 9, 7, 6, 3 };

Answer 2

Didn't the compiler give any error message/description? what did it say?