int i = 33;

bool[] bitmask = new[] {true, false, false, false, false, true};

BitArray bits = new BitArray(BitConverter.GetBytes(showGroup.HasValue));
List<String> showStrings = new List<string>();
for (int i = 0; i < bits.Length; i++)
{
    if(bits[i])
        showStrings.Add((i+1).ToString().PadLeft(2, '0'));
}

BitArray bits = new BitArray(System.BitConverter.GetBytes(showGroup.Value));

int val = 35;
List<string> showStrings = new List<string>();
for (int i = 0; i < 32; i++)
{
    if (( (1 << i) & val) > 0)
    {
        showStrings.Add((i + 1).ToString().PadLeft(2, '0'));
    }
}

01
02
06

bool IsSet(int val, int index)
{
    return (( (1 << (index-1)) & val) > 0);
}

// First define a bitmask enum for the bits you are interested in
[Flags]
public enum BitFlags
{
  Flag1 = 1,
  Flag2 = 2,
  Flag3 = 4,
  Flag4 = 8,
  Flag5 = 16
  // ...
}

int index = 0;
List<string> showStrings = new List<string>();
foreach(int flag in Enum.GetValues(typeof(BitFlags))cast<int>())
{
  index += 1;
  if ((input & flag) == flag)
    showStrings.Add(index.ToString().PadLeft(2, '0'));
}

int val = 33;
var bitarray = new BitArray(new[] { val });
var att = bitarray.Cast<bool>().ToArray();