Replace char with value in char array

Question

I think I found what the problem is. And I think my code fails when i try to replace a value in an array with another value from another array. I uses a for loop and then find out "i", the index and I try to replace one value in one array. There is some mixup in the indexes, but I can't figure it out!

What's below is as far as I have come.

There are some Norwegian words in there but don't let them confuse you. And I should tell you that I try to make a hangman game.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page 
{
char [] arrayOrd;
char[] bokstav;
char[] byggeOrd; 

protected void Page_Load(object sender, EventArgs e)
{
    //Session for remembering what word is gonna be guessed
    if (Session["arrayOrd"] != null)
    {
       arrayOrd = (char[])Session["arrayOrd"];
    }
    //This session contains the underscores
    if (Session["byggeOrd"] != null) {
        byggeOrd = (char[])Session["byggeOrd"];
    }
}
protected void Page_Unload(object sender, EventArgs e) 
{
    Session["arrayOrd"] = arrayOrd;
    Session["byggeOrd"] = byggeOrd;

}

protected void btnStart_Click(object sender, EventArgs e)
{
    string ord = txtOrd.Text.ToLower();
  arrayOrd = ord.ToCharArray();//Puts text from a textbox to an array called arrayOrd
  List<char> list = new List<char>();
    for (int i = 0; i < arrayOrd.Length; i++) {//Put underscores for as long arrayOrd is in a list.
      labRiktigBokstav.Text += "_ ";
      list.Add('_');
  }
  byggeOrd = list.ToArray(); //Put's the list that contains underscores in an array

}
//Checking if a letter is in the word
protected void btnSjekkOrd_Click(object sender, EventArgs e)
{
    string BSjekk = txtBokstavSjekk.Text.ToLower();
    bokstav = BSjekk.ToCharArray();
    if (arrayOrd.Contains(bokstav[0]))
    {
        for (int i = 0; i < arrayOrd.Length; i++)
        {
            if (arrayOrd[i] == bokstav[0])
            {
                byggeOrd[Array.IndexOf(byggeOrd, byggeOrd[i])] = arrayOrd[i]; //I think there is something wrong here!!!!!
                string resultat = new string(byggeOrd);
                labRiktigBokstav.Text = resultat;
            }
        }

    }
    else
    {
        //Print out that the guessed letter is wrong
    }
}
}

Answer 1

The following line is wrong:

byggeOrd[Array.IndexOf(byggeOrd, byggeOrd[i])] 

You are getting the index of a value through its very index.

int ind = Array.IndexOf(byggeOrd, byggeOrd[i]); 

The code above can retrieve any index. That's why it can modify an unintended value. You should replace it with

if (arrayOrd[i] == bokstav[0]){
    byggeOrd[i]= arrayOrd[i]; 
}