how to generate random characters in various text boxes

Question

I have tried variations of code for this, but some of the characters are repeating in the text boxes.

I want seven different characters in seven text boxes.

See picture for reference.... thank you in advance

enter image description here

Can you provide your code so far or the methods you've tried? — James, Mar 14 '15 at 22:06
We are not a code writing service. Please show us your code and we'll help fix it. — Enigmativity, Mar 14 '15 at 22:06

score 2 · Accepted Answer · answered Mar 14 '15 at 22:15

2

Random rnd = new Random();
var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
var sevenRandomChars = chars.OrderBy(_ => rnd.Next()).Take(7).ToList();

answered Mar 14 '15 at 22:15

EZI

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Are you sure your algorithm doesn't fall in the http://stackoverflow.com/questions/859253/why-does-this-simple-shuffle-algorithm-produce-biased-results-what-is-a-simple – xanatos Mar 14 '15 at 22:24
@xanatos Sorry, but yes, I am sure. (I have already read that http://ericlippert.com/2011/01/20/bad-comparisons-part-one/) – EZI Mar 14 '15 at 22:25
I've given a little thought... It is a little biased, but not so much. [OrderBy](https://msdn.microsoft.com/en-us/library/bb534966%28v=vs.110%29.aspx) is guaranteed to be stable (`This method performs a stable sort; that is, if the keys of two elements are equal, the order of the elements is preserved`), so if two elements gets the same `rnd.Next()` value, the one with a lower index is guaranteed to remain with the lower index. So elements on top have a little more chance to remain on top. But the bias is very very small for small arrays. – xanatos Mar 14 '15 at 22:36
@xanatos you may try it with a very large array :) `Enumerable.Range(0,10000000).OrderBy(_ => rnd.Next()).Take(7).ToList()` – EZI Mar 14 '15 at 22:42
No, it's easier to reduce the maximum value of `rnd.Next()`, in this way the collisions will raise. – xanatos Mar 14 '15 at 22:45
@xanatos OK, do it. Why don't you try it instead of posting a lot of comments. Do your tests and post the results. – EZI Mar 14 '15 at 22:50
I have tested this approach. There is no bias. – Enigmativity Mar 14 '15 at 23:02
textBox1.Text = letters[0].ToString(); textBox2.Text = letters[1].ToString(); textBox3.Text = letters[2].ToString(); textBox4.Text = letters[3].ToString(); textBox5.Text = letters[4].ToString(); textBox6.Text = letters[5].ToString(); textBox7.Text = letters[6].ToString(); I use this line after ur code letters.removeAt(i); its work fine but when I am hitting button for the second time it is not generating any thing plzz help ..... @xanatos – Rajsekhar pakalapati Mar 15 '15 at 05:47
@EZI Done http://pastebin.com/5CDnUxPG For an array of 3 elements, you do need at least r.Next(512) before having an unbiased shuffle. For 5 elements, at least r.Next(1024). As I've told, increasing the range of the random number generator makes the shuffler less biased. – xanatos Mar 15 '15 at 08:31

xanatos · Answer 2 · 2015-03-14T22:19:33.477

The simplest way is:

// The 26 letters, A...Z, in a char[] array
char[] letters = Enumerable.Range(0, 26).Select(x => (char)('A' + x)).ToArray();

Take all the 26 upper case letters

// http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
public static void Shuffle<T>(IList<T> list, Random r)
{
    for (int i = list.Count - 1; i > 0; i--)
    {
        int j = r.Next(0, i + 1);

        // Do the swap
        T temp = list[i];
        list[i] = list[j];
        list[j] = temp;
    }
}

// This is the method that does the shuffling
Shuffle(letters, new Random());

Shuffle them with the Fisher-Yates algorithm,

and take the first 7 elements of the shuffled letters array letters[0]...letters[6]. In this way you are gauranteed that the letters are unique, and that each letter has the same chance of being used.

An even easier way to do it:

// The 26 letters, A...Z, in a List<char>!
List<char> letters = Enumerable.Range(0, 26).Select(x => (char)('A' + x)).ToList();

Random r = new Random();

// The letters you "select"
char[] usedLetters = new char[7];

for (int i = 0; i < usedLetters.Length; i++)
{
    int j = r.Next(0, letters.Count);
    usedLetters[i] = letters[j];

    // When you select a letter, you remove it!
    letters.RemoveAt(i);
}

When you select a letter, you remove it. In this way any one letter can be used 0...1 times.

how to generate random characters in various text boxes

2 Answers2