一個簡單的十六進位制解碼器

以下 C# 語言程式（hexdecoder.cs）讀取內容為十六進位制數字的字串的文字檔案，輸出到二進位制檔案中。輸入檔案可以有多行，每行的長度可以不同，要求檔案的總長度為偶數。

using System;
using System.IO;
using System.Text;

static class Hexdecoder
{
  static int HexChar2Int(char c)
  {
    if (c >= '0' && c <= '9') return c - '0';
    if (c >= 'A' && c <= 'F') return c - 'A' + 10;
    if (c >= 'a' && c <= 'f') return c - 'a' + 10;
    throw new Exception("Invalid hex char: [" + c + "]");
  }

  static byte GetByte(string s, int i)
  {
    return (byte)(HexChar2Int(s[2 * i]) * 16 + HexChar2Int(s[2 * i + 1]));
  }

  static void Main(string[] args)
  {
    try {
      if (args.Length != 2) throw new Exception("Usage: hexdecoder.exe input-file output-file");
      var sb = new StringBuilder();
      foreach (var s in File.ReadLines(args[0])) sb.Append(s.Trim());
      using (var sw = new BinaryWriter(File.OpenWrite(args[1]))) {
        var s = sb.ToString();
        if (s.Length % 2 != 0) throw new Exception("Total length must be even number");
        var bs = new byte[s.Length / 2];
        for (var i = 0; i < bs.Length; i++) bs[i] = GetByte(s, i);
        sw.Write(bs);
      }
    } catch (Exception ex) {
      Console.WriteLine((ex.Message.StartsWith("Usage: ") ? "" : "Error: ") + ex.Message);
    }
  }
}