Parsing and operating on a value iteratively

ParseIteratively.cs

public static int[] ParseIteratively(string data)
{
  var results = new List<int>();
  var sum = 0;
  foreach (var cmd in data)
  {
    switch (cmd)
    {
      case 'i':
        sum++;
        break;
      case 'd':
        sum--;
        break;
      case 's':
        sum = sum * sum;
        break;
      case 'o':
        results.Add(sum);
        break;
    }
  }
  return results.ToArray();
}