using System;
using System.Collections;
using System.IO;

// Reads a text file and computes the frequencies of
// ASCII characters in it.
class CharacterStat {
  
  static void Main(string[] arg) {
    BitArray used = new BitArray(128);
    if (arg.Length > 0) {
      //--- read text and count characters
      string fileName = arg[0];
      StreamReader r = File.OpenText(fileName);
      int ch = r.Read();
      while (ch >= 0) {
        if (0 <= ch && ch < 128) used[ch] = true;
        ch = r.Read();
      }
      r.Close();
      //--- output character frequencies
      Console.WriteLine("The following ASCII characters occur in {0}:", fileName);
      for (int i = ' '; i < 127; i++)
        if (used[i]) Console.Write((char)i + " ");
    } else {
      Console.WriteLine("-- no input file specified");
    }
  }
}