Trouble converting C++ method to C#

Question

I'm trying to translate a C++ method that uses a homegrown form of encryption. But I don't understand what Buffer[x] and Input[x] are doing? As a C# developer (beginner at that), It looks like they should be arrays but they aren't declared as such. Can anyone explain please?

The input string "{x;ƒ~sq{j|tLtuq" translates to "MY SOFTWARE INC"

AnsiString __fastcall TMyMain::Decode(AnsiString Input)
{
  int error[] = { 2, 9, 5, 4, 1, 6, 7, 12, 19, 3, 1, 0, 21, 17 };
  int x;
  AnsiString Buffer = Input;

  if (encoded!=0)
  {
    int count = 0;

    for(x=Input.Length();x>=1;x--)
    {
      Buffer[x] = Input[x]-48+error[count];
      count++;
      if (count>=14)
        count=0;
    }
  }

  return Buffer;
}

Answer 1

Here's how I'd translate it. Note I have no idea where encoded comes from, so I left that out. The trick is to use a StringBuilder for your buffer so you can mutate the characters, another options would be a char array.

public static string Decode(string input)
{
    int[] error = { 2, 9, 5, 4, 1, 6, 7, 12, 19, 3, 1, 0, 21, 17 };
    StringBuilder buffer = new StringBuilder(input);

    int count = 0;
    for (int x = input.Length - 1; x >= 0; x--) {
        buffer[x] = (char)(input[x] - 48 + error[count]);
        count++;
        if (count >= 14)
            count = 0;
    }

    return buffer.ToString();
}

This however outputs "MY TOFTWARE INC" for the input "{x;ƒ~sq{j|tLtuq", so I'm not exactly sure if the issue is with your string or the code.

Answer 2

I've come up with this, but it doesn't quite return the expected results. Are you sure of the input string?

Input and output is string.

var encoded = true;
var input = "{x;ƒ~sq{j|tLtuq";
var output = Decode(input);
Console.WriteLine($"input \"{input}\", output \"{output}\"");

private static string Decode(string input)
{
    int[] error = { 2, 9, 5, 4, 1, 6, 7, 12, 19, 3, 1, 0, 21, 17 };
    var buffer = new char[input.Length];

    if (encoded)
    {
        int count = 0;

        for(var x=input.Length-1;x>=0;x--)
        {
            buffer[x] = (char) ((Convert.ToInt16(input[x])-48 + error[count]) & 0xFF);
            count++;
            if (count>=error.Length)
                count=0;
        }
        return new string(buffer)
    }
    return input;
}

Calling this writes the following to the console:

input "{x;ƒ~sq{j|tLtuq", output "MY bOFTWARE INC"

Answer 3

I don't know if it helps but after some reverse engeneering you could use the following errors array (with the StringBuilder implementation) to dispaly the proper information.

int[] error = { 2, 9, 5, 4, 1, 6, 7, 12, 19, 3, 1, -6, 21, 17 };//MY SOFTWARE INC

It has to do with how characters were encoded in c++ vs c# so you could try to play around with System.Text.Encoding .