Develop Reference

random binary of one million bit file size

I want to generate a one million bit random binary but my problem is that the code take to much time and not execute why that happen?
string result1 = "";
Random rand = new Random();
for (int i = 0; i < 1000000; i++)
{
result1 += ((rand.Next() % 2 == 0) ? "0" : "1");
}
textBox1.Text = result1.ToString();

Concatenating strings is an O(N) operation. Strings are immutable, so when you add to a string the new value is copied into a new string, which requires iterating the previous string. Since you're adding a value for each iteration, the amount that has to be read each time grows with each addition, leading to a performance of O(N^2). Since your N is 1,000,000 this takes a very, very long time, and probably is eating all of the memory you have storing these intermediary throw-away strings.
The normal solution when building a string with an arbitrary number of inputs is to instead use a StringBuilder. Although, a 1,000,000 character bit string is still.. unwieldy. Assuming a bitstring is what you want/need, you can change your code to something like the following and have a much more performant solution.
public string GetGiantBitString() {
var sb = new StringBuilder();
var rand = new Random();
for(var i = 0; i < 1_000_000; i++) {
sb.Append(rand.Next() % 2);
}
return sb.ToString();
}

This works for me, it takes about 0.035 seconds on my box:
private static IEnumerable<Byte> MillionBits()
{
var rand = new RNGCryptoServiceProvider();
//a million bits is 125,000 bytes, so
var bytes = new List<byte>(125000);
for (var i = 0; i < 125; ++i)
{
byte[] tempBytes = new byte[1000];
rand.GetBytes(tempBytes);
bytes.AddRange(tempBytes);
}
return bytes;
}
private static string BytesAsString(IEnumerable<Byte> bytes)
{
var buffer = new StringBuilder();
foreach (var byt in bytes)
{
buffer.Append(Convert.ToString(byt, 2).PadLeft(8, '0'));
}
return buffer.ToString();
}
and then:
var myStopWatch = new Stopwatch();
myStopWatch.Start();
var lotsOfBytes = MillionBits();
var bigString = BytesAsString(lotsOfBytes);
var len = bigString.Length;
var elapsed = myStopWatch.Elapsed;
The len variable was a million, the string looked like it was all 1s and 0s.
If you really want to fill your textbox full of ones and zeros, just set its Text property to bigString.

Cryptograhically random unique strings

In this answer, the below code was posted for creating unique random alphanumeric strings. Could someone clarify for me how exactly they are ensured to be unique in this code and to what extent these are unique? If I rerun this method on different occasions would I still get unique strings?
Or did I just misunderstand the reply and these are not generating unique keys at all, only random?
I already asked this in a comment to that answer but the user seems to be inactive.
public static string GetUniqueKey()
{
int maxSize = 8;
char[] chars = new char[62];
string a;
a = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
chars = a.ToCharArray();
int size = maxSize;
byte[] data = new byte[1];
RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider();
crypto.GetNonZeroBytes(data);
size = maxSize;
data = new byte[size];
crypto.GetNonZeroBytes(data);
StringBuilder result = new StringBuilder(size);
foreach (byte b in data)
{ result.Append(chars[b % (chars.Length - 1)]); }
return result.ToString();
}

There is nothing in the code that guarantees that the result is unique. To get a unique value you either have to keep all previous values so that you can check for duplicates, or use a lot longer codes so that duplicates are practically impossible (e.g. a GUID). The code contains less than 48 bits of information, which is a lot less than the 128 bits of a GUID.
The string is just random, and although a crypto strength random generator is used, that is ruined by how the code is generated from the random data. There are some issues in the code:
A char array is created, that is just thrown away and replaced with another.
A one byte array of random data is created for no apparent reason at all, as it's not used for anything.
The GetNonZeroBytes method is used instead of the GetBytes method, which adds a skew to the distribution of characters as the code does nothing to handle the lack of zero values.
The modulo (%) operator is used to reduce the random number down to the number of characters used, but the random number can't be evenly divided into the number of characters, which also adds a skew to the distribution of characters.
chars.Length - 1 is used instead of chars.Length when the number is reduced, which means that only 61 of the predefined 62 characters can occur in the string.
Although those issues are minor, they are important when you are dealing with crypo strength randomness.
A version of the code that would produce a string without those issues, and give a code with enough information to be considered practically unique:
public static string GetUniqueKey() {
int size = 16;
byte[] data = new byte[size];
RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider();
crypto.GetBytes(data);
return BitConverter.ToString(data).Replace("-", String.Empty);
}

Uniqueness and randomness are mutually exclusive concepts. If a random number generator is truly random, then it can return the same value. If values are truly unique, although they may not be deterministic, they certainly aren't truly random, because every value generated removes a value from the pool of allowed values. This means that every run affects the outcome of subsequent runs, and at a certain point the pool is exhausted (barring of course the possibility of an infinitely-sized pool of allowed values, but the only way to avoid collisions in such a pool would be the use of a deterministic method of choosing values).
The code you're showing generates values that are very random, but not 100% guaranteed to be unique. After enough runs, there will be a collision.

I need to generate 7 characters of an alphanumeric string. With a small search, I wrote the below code. Performance results are uploaded above
I have used hashtable Class to guarantee uniqueness and also used RNGCryptoServiceProvider Class to get high-quality random chars
results of generating 100.000 - 1.000.000 - 10.000.000 sample
Generating unique strings;
thanks to nipul parikh
public static Tuple<List<string>, List<string>> GenerateUniqueList(int count)
{
uniqueHashTable = new Hashtable();
nonUniqueList = new List<string>();
uniqueList = new List<string>();
for (int i = 0; i < count; i++)
{
isUniqueGenerated = false;
while (!isUniqueGenerated)
{
uniqueStr = GetUniqueKey();
try
{
uniqueHashTable.Add(uniqueStr, "");
isUniqueGenerated = true;
}
catch (Exception ex)
{
nonUniqueList.Add(uniqueStr);
// Non-unique generated
}
}
}
uniqueList = uniqueHashTable.Keys.Cast<string>().ToList();
return new Tuple<List<string>, List<string>>(uniqueList, nonUniqueList);
}
public static string GetUniqueKey()
{
int size = 7;
char[] chars = new char[62];
string a = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
chars = a.ToCharArray();
RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider();
byte[] data = new byte[size];
crypto.GetNonZeroBytes(data);
StringBuilder result = new StringBuilder(size);
foreach (byte b in data)
result.Append(chars[b % (chars.Length - 1)]);
return Convert.ToString(result);
}
Whole Console Application Code below;
class Program
{
static string uniqueStr;
static Stopwatch stopwatch;
static bool isUniqueGenerated;
static Hashtable uniqueHashTable;
static List<string> uniqueList;
static List<string> nonUniqueList;
static Tuple<List<string>, List<string>> generatedTuple;
static void Main(string[] args)
{
int i = 0, y = 0, count = 100000;
while (i < 10 && y < 4)
{
stopwatch = new Stopwatch();
stopwatch.Start();
generatedTuple = GenerateUniqueList(count);
stopwatch.Stop();
Console.WriteLine("Time elapsed: {0} --- {1} Unique --- {2} nonUnique",
stopwatch.Elapsed,
generatedTuple.Item1.Count().ToFormattedInt(),
generatedTuple.Item2.Count().ToFormattedInt());
i++;
if (i == 9)
{
Console.WriteLine(string.Empty);
y++;
count *= 10;
i = 0;
}
}
Console.ReadLine();
}
public static Tuple<List<string>, List<string>> GenerateUniqueList(int count)
{
uniqueHashTable = new Hashtable();
nonUniqueList = new List<string>();
uniqueList = new List<string>();
for (int i = 0; i < count; i++)
{
isUniqueGenerated = false;
while (!isUniqueGenerated)
{
uniqueStr = GetUniqueKey();
try
{
uniqueHashTable.Add(uniqueStr, "");
isUniqueGenerated = true;
}
catch (Exception ex)
{
nonUniqueList.Add(uniqueStr);
// Non-unique generated
}
}
}
uniqueList = uniqueHashTable.Keys.Cast<string>().ToList();
return new Tuple<List<string>, List<string>>(uniqueList, nonUniqueList);
}
public static string GetUniqueKey()
{
int size = 7;
char[] chars = new char[62];
string a = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
chars = a.ToCharArray();
RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider();
byte[] data = new byte[size];
crypto.GetNonZeroBytes(data);
StringBuilder result = new StringBuilder(size);
foreach (byte b in data)
result.Append(chars[b % (chars.Length - 1)]);
return Convert.ToString(result);
}
}
public static class IntExtensions
{
public static string ToFormattedInt(this int value)
{
return string.Format(CultureInfo.InvariantCulture, "{0:0,0}", value);
}
}

Using strictly alphanumeric characters restricts the pool you draw from to 62. Using the complete printable character set(ASCII 32-126) increases your pool to 94, decreasing the likelihood of collision and eliminating creating the pool separately.

random number gen, loop and store

How can I implement this so it is always ten numbers in length and how would I store n and r, loop 10 times, and store each loop aswell?
loop the random generator 10x to create 2x10 multiple 10 digit numbers.
namespace ConsoleApplication1
{
class Program
{
static void Main()
{
F();
F();
}
static Random _r = new Random();
static void F()
{
int n = _r.Next();
int r = _r.Next();
Console.WriteLine(n);
Console.WriteLine(r);
Console.ReadLine();
}
}

Something like this may be what you're looking for?
Though I'm not keen on the naming conventions, I'm not sure what these apply to, so can't exactly name them relevantly myself...
static int[] randomNumberArray0 = new int[10];
static int[] randomNumberArray1 = new int[10];
static Random random = new Random();
static void PopulateRandomNumberArrays()
{
for (int i = 0; i < 10; i++)
{
randomNumberArray0[i] = random.Next();
randomNumberArray1[i] = random.Next();
}
}
Update:
To execute this method then further output the values at a later time, try this:
static void PrintRandomNumberArrayValues(int[] array)
{
for (int i = 0; i < array.Length; i++)
{
Console.WriteLine("{0}", array[i]);
}
Console.WriteLine();
}
static void Main()
{
PopulateRandomNumberArrays();
PrintRandomNumberArrayValues(randomNumberArray0);
PrintRandomNumberArrayValues(randomNumberArray1);
Console.WriteLine("Press any key to exit...");
Console.ReadKey();
}
Output would look something like this:
2044334973
153458690
1271210885
734397658
746062572
162210281
1091625245
123317926
410432738
989880682
866647035
481104609
834599031
1153970253
94252627
1041485031
1934449666
414036889
1886559958
2083967380
Further update:
For the generated values to be constrained to 10 digits in length, it means the minimum generated value must be larger than 999999999 and, since an int has a max value of 2,147,483,647, smaller or equal to that, so:
for (int i = 0; i < 10; i++)
{
randomNumberArray0[i] = random.Next(1000000000, int.MaxValue);
randomNumberArray1[i] = random.Next(1000000000, int.MaxValue);
}
I have a feeling this still may not satisfy your needs though, as what I see coming next is that the numbers should be able to be represented as 0000000001, for instance - let's see.
Yet another update:
As I thought, the value of numbers should not be constrained to our specified range, but rather only the output formatted appropriately; thus generation reverts to my original suggestion and printing is altered as so:
Console.WriteLine("{0:D10}", array[i]);

I guess you could use a list of tuples to store and return your results:
static List<Tuple<int,int>> F()
{
var results = new List<Tuple<int,int>> ();
for (int i = 0; i < 10; i++)
{
results.Add(new Tuple<int, int>(_r.Next(), _r.Next()));
}
return results;
}

C#: random number issue

See the following:
for (int i=0; i<2; i++) {
// do some stuff
r = new Random((int)DateTime.Now.Ticks);
iRandom = r.Next(30000);
// do some other stuff
}
Don't ask me how, but iRandom is sometimes the same for both iterations of the loop. I need iRandom to be different for each iteration. How do I do this?

Change your loop to this:
r = new Random((int)DateTime.Now.Ticks);
for (int i=0; i<2; i++) {
// do some stuff
iRandom = r.Next(30000);
// do some other stuff
}
In other words, put the creation of the Random object outside the loop.

For some surprises with Math.Random doubles versus RNGCryptoServiceProvider, try plotting the results of the following (say, using a spreadsheet). This code will run in LinqPad (www.LinqPad.net). It's worth a look :)
void Main()
{
{
var ds = Enumerable.Range(1, 30).Select(i => new Random(i).NextDouble());
ds.Dump();
}
{
var csp = new System.Security.Cryptography.RNGCryptoServiceProvider();
var bs = new byte[8 * 30];
var ds = new double[30];
csp.GetBytes(bs);
for (var i = 0; i < 30; i++)
{
var d = BitConverter.ToDouble(bs, i * 8);
while (d == 0D || Double.IsNaN(d))
{
var bytes = new byte[8];
csp.GetBytes(bytes);
d = BitConverter.ToDouble(bs, 0);
}
ds[i] = Math.Log10(Math.Abs(d));
}
ds.Dump();
}
}

try creating your Random with a non time-based seed, otherwise the seed may be the same (and the random number same also)
for (int i = 0; i < 2; i++)
{
// do some stuff
r = new Random(Guid.NewGuid().GetHashCode());
iRandom = r.Next(30000);
// do some other stuff
}

A REALLY nice explanation: http://msdn.microsoft.com/en-us/library/system.random.aspx

Try seeding with a new Guid, or, better yet, use the Cryto provider... Here's a Stko article with code
Best way to seed Random() in singleton

DateTime.Now.Ticks is a Int64 type. If you cast to an int, it could be casting to the same value for the seed and therefore giving you the same random number.
No need to reseed or recreate the Random object once it is created. Just reuse the object and obtain the next random number.

generating a batch of random passwords

Generating a random password is easy. but generating a batch is more difficult.
public static string getRandomPassword(int letters, int getallen) {
//int letters = 8;
//int getallen = 5;
char[] letterdeel = new char[letters];
int minGetal = (int)Math.Pow(10, getallen - 1);
int maxGetal = (int)Math.Pow(10, getallen);
string password;
Random r = new Random();
int test = (int)(DateTime.Now.Ticks);
for (int i = 0; i < letters; i++) {
r = new Random((int)(DateTime.Now.Ticks) + i);
bool capital = r.Next(2) == 0 ? true : false;
if (capital) {
letterdeel[i] = (char)r.Next(65, 91);
} else {
letterdeel[i] = (char)r.Next(97, 123);
}
}
password = new string(letterdeel);
password += r.Next(minGetal, maxGetal);
return password;
}
this is my method, the passwords should be in a certain letter-number format.
this works fine, however if i have a for loop pulling 100 passwords from this method, in my array i have 5-8 the same passwords, then again 5-8 the same pass.
i know WHY this is, because of the random function and the clock it depends on, but how do i fix this?

Move Random r to outside the method if you are repeatedly calling it. You are going to be hitting it several times in the same relative timeframe, so you are going to be generating the same seeds. You also want to get rid of the line below. It is unnecessary, and (again), with the nature of DateTime.Now, you would just continue to generate the same sequence of "random" numbers.
r = new Random((int)(DateTime.Now.Ticks) + i);

Define your random number generator as a static outside of the function.
How can I get true randomness in this class without Thread.Sleep(300)?

Use a set rather than whatever collection you store into and don't loop 100 times but until the set has 100 items in it.