Develop Reference

Reverse a foreach loop action

I want to convert/find each of my string characters to (int) and reverse this operation.
I manage to do the first part,but the seconds one is giving me some problems.
string input;
string encrypt = ""; string decrypt = "";
input = textBox.Text;
foreach (char c in input)
{
int x = (int)c;
string s = x.ToString();
encrypt += s;
}
MessageBox.Show(encrypt);
foreach (int i in encrypt)
{
char c = (char)i;
string s = c.ToString();
decrypt += c;
}
MessageBox.Show(decrypt);
Thanks!

Here is a fixed program according to my advise above
string encrypt = ""; string decrypt = "";
string input = Console.ReadLine();
var length = input.Length;
int[] converted = new int[length];
for (int index = 0; index < length; index++)
{
int x = input[index];
string s = x.ToString();
encrypt += s;
converted[index] = x;
}
Console.WriteLine(encrypt);
for (int index = 0; index < converted.Length; index++)
{
char c = (char)converted[index];
string s = c.ToString();
decrypt += s;
}
Console.WriteLine(decrypt);

This will not work as is, because you're adding numbers to a string with no padding.
Let's assume the first three letter's values are '1','2','3', you'll have a string with "123".
Now, if you know each letter is 1 int length, you're good, but what happens if 12 is valid? and 23?
This might not be a "real" issues in your case because the values will probably be all 2 ints long, but it's very lacking (unless it's homework, in which case, oh well ...)
The ascii values for the alphabet will go from 65 for A to 122 z.
You can either pad them (say 3 chars per number, so 065 for A, and so on), delimit them (have ".", and split the string on that), use an array (like shahar's suggestion), lists, etc etc ...

In Your scenario, encryption may give output as you expected but its hard to decrypt the encrypted text using such mechanism. so I just do some customization on your code and make it workable here.
i suggest a similar one here:
string input;
string encrypt = ""; string decrypt = "";
int charCount = 0;
input = "textBox.Text";
foreach (char c in input)
{
int x = (int)c;
string s = x.ToString("000");
encrypt += s;
charCount++;
}
// MessageBox.Show(encrypt);
while (encrypt.Length > 0)
{
int item = Int32.Parse(encrypt.Substring(0, 3));
encrypt = encrypt.Substring(3);
char c = (char)item;
string s = c.ToString();
decrypt += c;
}
Reason for your code is not working:
You have declared encrypt as string and iterate through each integer in that string value, it is quiet not possible.
if you make that loop to iterate through each characters in that string value again it gives confusion. as :
lets take S as your input. its equivalent int value is 114 so if you make a looping means it will give 1,1,4, you will not get s back from it.

Convert emoji to hex number

I'm trying to convert an emoji to an hex number or a string.
there is any way to convert this 👱 in this : 0x00000000D83DDC71L or D83DDC71
Edit
my code is this:
var bytes = Encoding.UTF8.GetBytes(emoji.ToString()); //emoji is 👱
var number = BitConverter.ToUInt32(bytes, 0); //number is 2610470896
var emojiCode = unicode.ToString("X"); // emojiCode is 9B989FF0
the problem is that i need my emojiCode to be D83DDC71
i hope is more clear now.

You have to do something like:
var str = "\uD83D\uDC71";
string res = BitConverter.ToString(Encoding.BigEndianUnicode.GetBytes(str)).Replace("-", "");
Note that you want your Unicode string to be in "big endian" mode (so Encoding.BigEndianUnicode)
Probably easier without going through the Encoding conversion:
string res = string.Concat(str.Select(x => ((ushort)x).ToString("X4")));
(ushort and char are nearly the same thing, but ushort is built to be formatted as a number, while char is built to be formatted as a character)

Emoji Unicode is not a single hex number, and it only encoding by UTF32.
So you could split it, like this:
byte[] utfBytes = System.Text.Encoding.UTF32.GetBytes("👱");
print(utfBytes.Length);
for (int i = 0; i < utfBytes.Length; i += 4)
{
if (i != 0) result += '-';
result += System.BitConverter.ToInt32(utfBytes, i).ToString("x2").ToUpper();
}

string values to byte array without converting

I'm trying to put the values of a string into a byte array with out changing the characters. This is because the string is in fact a byte representation of the data.
The goal is to move the input string into a byte array and then convert the byte array using:
string result = System.Text.Encoding.UTF8.GetString(data);
I hope someone can help me although I know it´s not a very good description.
EDIT:
And maybe I should explain that what I´m working on is a simple windows form with a textbox where users can copy the encoded data into it and then click preview to see the decoded data.
EDIT:
A little more code:
(inputText is a textbox)
private void button1_Click(object sender, EventArgs e)
{
string inputString = this.inputText.Text;
byte[] input = new byte[inputString.Length];
for (int i = 0; i < inputString.Length; i++)
{
input[i] = inputString[i];
}
string output = base64Decode(input);
this.inputText.Text = "";
this.inputText.Text = output;
}
This is a part of a windows form and it includes a rich text box. This code doesn´t work because it won´t let me convert type char to byte.
But if I change the line to :
private void button1_Click(object sender, EventArgs e)
{
string inputString = this.inputText.Text;
byte[] input = new byte[inputString.Length];
for (int i = 0; i < inputString.Length; i++)
{
input[i] = (byte)inputString[i];
}
string output = base64Decode(input);
this.inputText.Text = "";
this.inputText.Text = output;
}
It encodes the value and I don´t want that. I hope this explains a little bit better what I´m trying to do.
EDIT: The base64Decode function:
public string base64Decode(byte[] data)
{
try
{
string result = System.Text.Encoding.UTF8.GetString(data);
return result;
}
catch (Exception e)
{
throw new Exception("Error in base64Decode" + e.Message);
}
}
The string is not encoded using base64 just to be clear. This is just bad naming on my behalf.
Note this is just one line of input.
I've got it. The problem was I was always trying to decode the wrong format. I feel very stupid because when I posted the example input I saw this had to be hex and it was so from then on it was easy. I used this site for reference:
http://msdn.microsoft.com/en-us/library/bb311038.aspx
My code:
public string[] getHexValues(string s)
{
int j = 0;
string[] hex = new String[s.Length/2];
for (int i = 0; i < s.Length-2; i += 2)
{
string temp = s.Substring(i, 2);
this.inputText.Text = temp;
if (temp.Equals("0x")) ;
else
{
hex[j] = temp;
j++;
}
}
return hex;
}
public string convertFromHex(string[] hex)
{
string result = null;
for (int i = 0; i < hex.Length; i++)
{
int value = Convert.ToInt32(hex[i], 16);
result += Char.ConvertFromUtf32(value);
}
return result;
}
I feel quite dumb right now but thanks to everyone who helped, especially #Jon Skeet.

Are you saying you have something like this:
string s = "48656c6c6f2c20776f726c6421";
and you want these values as a byte array? Then:
public IEnumerable<byte> GetBytesFromByteString(string s) {
for (int index = 0; index < s.Length; index += 2) {
yield return Convert.ToByte(s.Substring(index, 2), 16);
}
}
Usage:
string s = "48656c6c6f2c20776f726c6421";
var bytes = GetBytesFromByteString(s).ToArray();
Note that the output of
Console.WriteLine(System.Text.ASCIIEncoding.ASCII.GetString(bytes));
is
Hello, world!
You obviously need to make the above method a lot safer.

Encoding has the reverse method:
byte[] data = System.Text.Encoding.UTF8.GetBytes(originalString);
string result = System.Text.Encoding.UTF8.GetString(data);
Debug.Assert(result == originalString);
But what you mean 'without converting' is unclear.

One way to do it would be to write:
string s = new string(bytes.Select(x => (char)c).ToArray());
That will give you a string that has one character for every single byte in the array.
Another way is to use an 8-bit character encoding. For example:
var MyEncoding = Encoding.GetEncoding("windows-1252");
string s = MyEncoding.GetString(bytes);
I'm think that Windows-1252 defines all 256 characters, although I'm not certain. If it doesn't, you're going to end up with converted characters. You should be able to find an 8-bit encoding that will do this without any conversion. But you're probably better off using the byte-to-character loop above.

If anyone still needs it this worked for me:
byte[] result = Convert.FromBase64String(str);

Have you tried:
string s = "....";
System.Text.UTF8Encoding.UTF8.GetBytes(s);

code translation: repeating a string until some maximum

I was wondering if you could tell me what the most efficient way to repeat a string would be. I need to create a string 33554432 bytes long, repeating the string "hello, world" until it fills that buffer. What is the best way to do it, C is easy in this case:
for (i = 0; i < BIGSTRINGLEN - step; i += step)
memcpy(bigstring+i, *s, step);
Thanks.

An efficient way would be to use a StringBuilder:
string text = "hello, world";
StringBuilder builder = new StringBuilder(BIGSTRINGLEN);
while (builder.Length + text.Length <= BIGSTRINGLEN) {
builder.Append(text);
}
string result = builder.ToString();

First, do you want the string to be 33554432 bytes long, or characters long? .NET and C# use 16-bit characters, so they are not equivalent.
If you want 33554432 characters, naive solution would be string concatenation. See Frédéric Hamidi's answer.
If you want bytes, you will need to do something a bit more interesting:
int targetLength = 33554432;
string filler = "hello, world";
byte[] target = new byte[targetLength];
// Convert filler to bytes. Can use other encodings here.
// I am using ASCII to match C++ output.
byte[] fillerBytes = Encoding.ASCII.GetBytes(filler);
//byte[] fillerBytes = Encoding.Unicode.GetBytes(filler);
//byte[] fillerBytes = Encoding.UTF8.GetBytes(filler);
int position = 0;
while((position + fillerBytes.Length) < target.Length)
{
fillerBytes.CopyTo(target, position);
position += fillerBytes.Length;
}
// At this point, need to possibly do a partial copy.
if (position < target.Length)
{
int bytesNecessary = target.Length - position;
Array.Copy(fillerBytes, 0, target, position, bytesNecessary);
}

I don't know if it's the most efficient way, but if you're using .NET 3.5 or later, this could work:
String.Join("", System.Linq.Enumerable.Repeat("hello, world", 2796203).ToArray()).Substring(0, 33554432);
If the length you want is dynamic, then you can replace some of the hard-coded numbers with simple math.

What about this? Set the StringBuilder to the max expected size and then add the desired string as long as adding another one will not exceed the desired max size.
StringBuilder sb = new StringBuilder(33554432);
int max = sb.MaxCapacity;
String hello = "hello, world";
while (sb.Length + hello.Length <= max)
{
sb.Append(hello);
}
string longString = sb.ToString();

This avoids a loop that repeatedly adds the string. Instead, I "double" the string until it gets close to the right length and then I put the "doubled" pieces together appropriately.
static string Repeat(string s, int length) {
if (length < s.Length) {
return s.Substring(0, length);
}
var list = new List<string>();
StringBuilder t = new StringBuilder(s);
do {
string temp = t.ToString();
list.Add(temp);
t.Append(temp);
} while(t.Length < length);
int index = list.Count - 1;
StringBuilder sb = new StringBuilder(length);
while (sb.Length < length) {
while (list[index].Length > length) {
index--;
}
if (list[index].Length <= length - sb.Length) {
sb.Append(list[index]);
}
else {
sb.Append(list[index].Substring(0, length - sb.Length));
}
}
return sb.ToString();
}
So, for example, on input ("Hello, world!", 64) we build the strings
13: Hello, World!
26: Hello, World!Hello, World!
52: Hello, World!Hello, World!Hello, World!Hello, World!
Then we would build the result by concatenating the string of length 52 to the substring of length 12 of the string of length 13.
I am, of course, assuming that by bytes you meant length. Otherwise, you can easily modify the above using encodings to get what you want in terms of bytes.

Calculating info_hash from UrlEncoded query string

Basically, I'm building a small tracker for experimental purposes. I've gotten quite far, and am now working on the announce part.
What I really can't figure out is how I should decode the info_hash query string provided.
From the specification, it is a urlencoded 20-byte SHA1 hash, which made me write this code,
byte[] foo = Encoding.Default.GetBytes(HttpUtility.UrlDecode(infoHash));
string temp = "";
foreach (byte b in foo)
{
temp += b.ToString("X");
}
Which gives 'temp' the following value,
5D3F3F3F3F5E3F3F3F153FE4033683F55693468
The first and last few characters are correct. This is the raw info_hash,
%5d%96%b6%f6%84%5e%ea%da%c5%15%c4%0e%403h%b9Ui4h
And this is what both uTorrent and my own tracker gives me as info_hash when generating it from the torrent file,
5D96B6F6845EEADAC515C40E403368B955693468
What am I doing wrong?

UrlDecode returns a string, but a SHA1 hash doesn't make sense if interpreted as (ANSI) string.
You need to decode the input string directly to an byte array, without the roundtrip to a string.
var s = "%5d%96%b6%f6%84%5e%ea%da%c5%15%c4%0e%403h%b9Ui4h";
var ms = new MemoryStream();
for (var i = 0; i < s.Length; i++)
{
if (s[i] == '%')
{
ms.WriteByte(
byte.Parse(s.Substring(i + 1, 2), NumberStyles.AllowHexSpecifier));
i += 2;
}
else if (s[i] < 128)
{
ms.WriteByte((byte)s[i]);
}
}
byte[] infoHash = ms.ToArray();
string temp = BitConverter.ToString(infoHash);
// "5D-96-B6-F6-84-5E-EA-DA-C5-15-C4-0E-40-33-68-B9-55-69-34-68"

HttpUtility.UrlDecodeToBytes