String to Binary in C#

Here you go:

public static byte[] ConvertToByteArray(string str, Encoding encoding)
{
    return encoding.GetBytes(str);
}

public static String ToBinary(Byte[] data)
{
    return string.Join(" ", data.Select(byt => Convert.ToString(byt, 2).PadLeft(8, '0')));
}

// Use any sort of encoding you like. 
var binaryString = ToBinary(ConvertToByteArray("Welcome, World!", Encoding.ASCII));

It sounds like you basically want to take an ASCII string, or more preferably, a byte[] (as you can encode your string to a byte[] using your preferred encoding mode) into a string of ones and zeros? i.e. 101010010010100100100101001010010100101001010010101000010111101101010

This will do that for you...

//Formats a byte[] into a binary string (010010010010100101010)
public string Format(byte[] data)
{
    //storage for the resulting string
    string result = string.Empty;
    //iterate through the byte[]
    foreach(byte value in data)
    {
        //storage for the individual byte
        string binarybyte = Convert.ToString(value, 2);
        //if the binarybyte is not 8 characters long, its not a proper result
        while(binarybyte.Length < 8)
        {
            //prepend the value with a 0
            binarybyte = "0" + binarybyte;
        }
        //append the binarybyte to the result
        result += binarybyte;
    }
    //return the result
    return result;
}

The following will give you the hex encoding for the low byte of each character, which looks like what you're asking for:

StringBuilder sb = new StringBuilder();
foreach (char c in asciiString)
{
    uint i = (uint)c;
    sb.AppendFormat("{0:X2}", (i & 0xff));
}
return sb.ToString();