Converting a String to a String of Binary

You can use the Convert method for that:

byte [] bytesToEncode = Encoding.UTF8.GetBytes (inputText);
string encodedText = Convert.ToBase64String (bytesToEncode);

If you can encode/decode a byte, e.g.

private static String ToBinary(Byte value) {
  StringBuilder Sb = new StringBuilder(8);

  Sb.Length = 8;

  for (int i = 0; i < 8; ++i) {
    Sb[7 - i] = (Char) ('0' + value % 2);

    value /= 2;
  }

  return Sb.ToString();
}

private static Byte FromBinary(String value) {
  int result = 0;

  for (int i = 0; i < value.Length; ++i)
    result = result * 2 + value[i] - '0';

  return (Byte) result;
}

You can easily encode/decode a whole string:

  // Encoding... 
  String source = "abc";

  // 011000010110001001100011
  String result = String.Join("", UTF8Encoding.UTF8.GetBytes(source).Select(x => ToBinary(x)));

  ... 

  // Decoding...
  List<Byte> codes = new List<Byte>();

  for (int i = 0; i < result.Length; i += 8) 
    codes.Add(FromBinary(result.Substring(i, 8)));

  // abc
  String sourceBack = UTF8Encoding.UTF8.GetString(codes.ToArray());

use

string str = "Welcome"; 
byte []arr = System.Text.Encoding.ASCII.GetBytes(str);