C# Display repeated letter in string

Question

I'm trying to figure out how to display the repeated letter in a string. For example if the entered string was "red house" it would show that the letter "e" was repeated, then it would be displayed in the label I created. This is a basic program, Here is what I've written thus far. Any help is appreciated.

private void button1_Click(object sender, EventArgs e)
    {
        string enteredWord = textBox1.Text;
        char letter;


        for (int index = 0; index < enteredWord.Length; index++) 
        {
            letter = enteredWord[index];

            if (letter == enteredWord[index])
            {
                label1.Text = (letter.ToString());
            }
            else
            { return; 

            }

Answer 1

You could also use Linq for that:

      var query = from l in enteredWord
                    group l by l into g
                    where g.Count() > 1
                    select new {  letter = g.Key, count = g.Count() };
        foreach (var item in query)
        {
            label1.Text += item.letter + " ";
        }

Answer 2

This should do what you're looking for:

    public static Dictionary<char, int> Count(string input)
    {
        Dictionary<char, int> d = new Dictionary<char, int>();
        foreach (char c in input)
        {
            if (d.Keys.Contains(c))
                d[c]++;
            else
                d.Add(c, 1);
        }
        return d;
    }

    static void Main(string[] args)
    {
        Dictionary<char, int> d = Count("Red House");
        foreach (char c in d.Keys)
        {
            Console.WriteLine("{0}: {1}", c, d[c]);
        }
        Console.ReadKey();
    }

Answer 3

Could build a HashSet and check each letter. I'm sure there's a more efficient way, but this should work: (untested)

string enteredWord = textBox1.Text;
HashSet<char> letters = new HashSet<char>();
foreach(char c in enteredWord)
{
    if (letters.Contains(c))
        label1.Text += c.ToString();
    else
        letters.Add(c);
}

EDIT: I suppose this will print out duplicates of the letters if they appear 3 or more times, but you get the idea.

Answer 4

I would suggest using a List and add the value if you have not encountered it, and update the textbox if you have already encountered it. For a future FYI, you could use a Dictionary if you need to know the exact counts, also.

    List<char> charactersThatHaveOccurred = new List<char>();
    string enteredWord = textBox1.Text;
    foreach(var character in enteredWord)
    {
        if(charactersThatHaveOccurred.Contains(character ))
            label1.Text += character ;
        else
            charactersThatHaveOccurred.Add(character );
    }

Answer 5

The first thing that comes to mind is:

List<char> repeats = enteredWord.Where(c1 => enteredWord.Count(c2 => c1 == c2) > 1).Distinct().ToList();

That will return a List<char> of all the repeated characters. You can grab the first one, or whatever you want.

It may not be optimal in terms of speed, but it's simple.

Answer 6

See other answers for better ways to solve this problem, but I'm trying to see what you were trying to do. (Note, the code below is very inefficient, using a HashSet of already seen characters would be my solution at it.)

Perhaps you're missing an inner for loop? Currently you assign something ( enteredword[index] ) to letter , and then immediately compare them. So you're comparing each letter to itself.

something like

    for (int index = 0; index < enteredWord.Length; index++) 
    {
        letter = enteredWord[index];

        for (int index2 = 0; index < enteredWord.Length; index++)
        {
            if (index != index2 && letter == enteredWord[index2])
            {
                label1.Text = (letter.ToString());
                return;
            }
        }
    }

Answer 7

           string s = "red house";   
            foreach (char c in s)
            {
                if (s.IndexOf(c) != s.LastIndexOf(c))
                {
                    label1.Text += c.ToString();
                }
                s.Replace(c.ToString(), string.Empty);
            }