Index out of bounds when it's in bounds

Question

I'm getting an index out of bounds error when I request the last element in the list for a C# Windows Form Application.

Does anyone know what might be causing this because it literally makes no sense whatsoever. It's as if the computer is miscalculating. The size is supposedly 17, but everything above index 5 gives an error. Once logic goes out the window, I've got nothing left. Perhaps there's something weird going on behind the scenes that someone else may have encountered before?

List<string> words = new List<string>();

        List<string> words = new List<string>();
        string word = "";
        int idx = 0;
        while (idx < notes.Length)
        {
            word += notes[idx];
            if (notes[idx] == ' ')
            {
                words.Add(word);
                word = "";
            }
            ++idx;
        }
        string notes1 = "";
        string notes2 = "";
        string notes3 = "";

        int one_third = words.Count / 3;
        int two_thirds = (words.Count / 3) * 2;

        int k;
        for (k = 0; k < one_third; k++)
            notes1 += words.ElementAt(k) + ' ';
        for (k = one_third; k < two_thirds; k++)
            notes2 += words[k] + ' ';
        for (k = two_thirds; k < words.Count; k++)
            notes3 += words[k] + ' ';

        notesLabel1.Text = notes1;
        notesLabel2.Text = notes2;
        notesLabel3.Text = notes3;

++++++++++++++++++++++++++++++++++++++++++++++

FOUND THE PROBLEM!!!!!!

Basically, I overworked myself yesterday so my brain was fried by the end of the day and I was irritable. The function code works just fine unless, like many have said, the notes string is empty. I knew that the notes string wasn't empty because it posts just fine without the +1 portion in the for-loop. BUT I FORGOT ABOUT ONE THING. The first 'item' that gets posted to the form is the first 'item' in the array I have in my program. Even though the item notes in question do indeed have 17 words, it's the second item in the list. The first item in the list gets posted when the application loads and I simply scroll over to the item with the 17 word notes. The first item that's posted doesn't have notes so the first time that function is called, the argument is an empty string. OOPS! feels dumb

Thanks, everyone!! I appreciate you taking the time to help fix my nonsense here. haha

Answer 1

The errors are fairly straightforward, and we can explain all the symptoms.

Firstly note that:

List<string> words = new List<string>();

gives you an EMPTY array for which words.Count == 0. In particular, note that words.ElementAt(0) will throw.

Ok so with this line (which throws):

string the_word = words.elementAt(words.Count - 1);

Clearly (words.Count - 1) is -1 and thus the error.

The following code DOES NOT throw an error:

for (k = 0; k < words.Count / 3; k++) notes1 += words.ElementAt(k) + ' ';

because the for loop runs while k < 0, and so the loop doesn't even execute a single iteration.

Now this one:

for (k = 0; k < words.Count / 3 + 1; k++) notes1 += words.ElementAt(k) + ' ';

This loop will run while k < 1 so it will execute once with k=0, and thus ElementAt(0) will throw because the array is empty.

Finally:

for (k = 0; k < words.Count; k++) notes1 += words.ElementAt(k);

Again this will not iterate even once. words.Count is 0, so it runs while k < 0 which means it doesn't iterate.

Answer 2

if words is empty, you are getting words.Count - 1 means -1, how can you do:

words.elementAt(-1);

Answer 3

Notice something in your code down below:

if (notes[idx] == ' ')
        {
            words.Add(word);
            word = "";
        }

You add to your words List when the notes is empty? like notes[idx] == ' '

Could it be testing if it is not empty before you add it, like?

if (!String.IsNullOrEmpty(notes[idx]))
        {
            words.Add(word);
            word = "";
        }

Just guessing.

Original Post:

Check the count first before doing elementAt, so instead of:

 string the_word = words.elementAt(words.Count - 1);

Do like :

 string the_word = words.Count>0 ? words.elementAt(words.Count - 1) : "";

And probably it would be good if you check it with messagebox just for debugging if the count is really 17 as you claim like:

 MessageBox.Show(words.Count);
 string the_word = words.Count>0 ? words.elementAt(words.Count - 1) : "";

Update:

I did a sampling in my own PC with the code below that came from your posting and it works with no error. Could it be that you're using multi-threading and it tries to change the value of your words List?

 List<string> words = new List<string>();
        String notes1="";

        int k;
        words.Add("The quick brown fox jumps over the lazy dog.");
        string the_word = words.ElementAt(words.Count - 1);
        MessageBox.Show(the_word);

        for (k = 0; k < words.Count / 3; k++)
        { notes1 += words.ElementAt(k) + ' '; }


        for (k = 0; k < words.Count / 3 + 1; k++)
        { notes1 += words.ElementAt(k) + ' '; }

Answer 4

If you're code only contains a single space, then it will only have one word in the array.

The result of one_third and two_thirds will then always be zero IF words.Count is less than 3. Which means the rest of your code will never find them.

When you add +1 to the words.count, then it will go outside the bounds of the array.

All in all this is a really round about (and error filled) way of splitting the notes.

UPDATE

I used the following test code:

        Char[] notes = "there are seventeen words in this list make the most of them because it really counts here".ToCharArray();

        List<string> words = new List<string>();
        string word = "";
        int idx = 0;
        while ( idx < notes.Length ) {
            word += notes[idx];
            if ( notes[idx] == ' ' ) {
                words.Add(word);
                word = "";
            }
            ++idx;
        }
        string notes1 = "";
        string notes2 = "";
        string notes3 = "";

        int one_third = words.Count / 3;
        int two_thirds = ( words.Count / 3 ) * 2;
        int k;

        for ( k = 0; k < one_third +1; k++ )
            notes1 += words.ElementAt(k) + ' ';

        for ( k = one_third; k < two_thirds; k++ )
            notes2 += words[k] + ' ';

        for ( k = two_thirds; k < words.Count; k++ )
            notes3 += words[k] + ' ';

        MessageBox.Show(notes1);

and had no errors. The result was not exactly what you normally expect, but there were no errors. Note that I put in the +1 that was the stated problem.

---

An alternative way to accomplish this is:

    String notes = "there are seventeen words in this list make the most of them because it really counts here";

    Int32 one_third = notes.Trim().Split(' ').Count() / 3 + 1;
    String matchString = @"^(\w+\b.*?){" + one_third.ToString() + "}";

    String notes1 = Regex.Match(notes, matchString).ToString();
    notes = notes.Remove(0, notes1.Count()).Trim();

    String notes2 = Regex.Match(notes, matchString).ToString();
    notes = notes.Remove(0, notes2.Count()).Trim();

    String notes3 = notes;

Answer 5

Sorry but you're just plain wrong.

The following code in a new console app outputs:

Some  nine  word
note  which  I'm
stretching  here  now

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace StackOverflow16491866 {
    class Program {
        static void Main(string[] args) {
            string notes = "Some nine word note which I'm stretching here now ";
            List<string> words = new List<string>();
            string word = "";
            int idx = 0;
            while (idx < notes.Length) {
                word += notes[idx];
                if (notes[idx] == ' ') {
                    words.Add(word);
                    word = "";
                }
                ++idx;
            }
            string notes1 = "";
            string notes2 = "";
            string notes3 = "";

            int one_third = words.Count / 3;
            int two_thirds = (words.Count / 3) * 2;

            int k;
            for (k = 0; k < one_third; k++)
                notes1 += words.ElementAt(k) + ' ';
            for (k = one_third; k < two_thirds; k++)
                notes2 += words[k] + ' ';
            for (k = two_thirds; k < words.Count; k++)
                notes3 += words[k] + ' ';

            Console.WriteLine(notes1);
            Console.WriteLine(notes2);
            Console.WriteLine(notes3);
            Console.ReadLine();

        }
    }
}

In short, your code works when notes is populated correctly.

Note that it requires a trailing space in notes to split into 3x3x3 instead of 2x2x5

The simplified form of your code is...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace StackOverflow16491866 {
    class Program {
        static void Main(string[] args) {
            string Notes = "Some nine word note which I'm stretching here now";
            List<string> Words = Notes.Split(' ').ToList();
            int WordsPerLine = (int)Words.Count/3;
            string Note1 = string.Join(" ", Words.GetRange(0, WordsPerLine));
            string Note2 = string.Join(" ", Words.GetRange(WordsPerLine, WordsPerLine));
            string Note3 = string.Join(" ", Words.GetRange(WordsPerLine * 2, Words.Count - WordsPerLine * 2 - 1));
            Console.WriteLine("{0}\n{1}\n{2}", Note1, Note2, Note3);
            Console.ReadLine();
        }
    }
}