For-Loop index gets reset to 0 after nested While-Loop

Question

As a coding execise, I'm working on a visualisation of different sorting algorithms. I have a button that pauses the algorithm and shows every item of the array as a bar-diagramm. To achive this, I have a nested while-loop inside of the two for-loops for the sorting. It loops throug, until I press the button again, a boolean variable gets set to true and the sorting continues.

However, after the programm exits the while loop, the two indecies of the for-loops (i and j) get reset to 0 and the sorting starts from the beginning again.

swap() and draw() are custom functions that do pretty much exactly what the name suggests.

Here's my code for the sorting:

for (i = 0; i < items.Count(); i++)
    {
        for (j = 0; j < items.Count() - 1 - i; j++)
        {
            //lbl_i.Text = Convert.ToString(i);
            //lbl_j.Text = Convert.ToString(j);

            if (items[j] > items[j + 1])
            {
                swap(j, j + 1); //swaps the items at two given indecies
                draw(); // draws the array to the picturebox
            }

            while (sorting == false) //the sorting is paused
            {
                Application.DoEvents();
            }
        }
    }

Any idea why this could happen?

I have a suspition that it could be a problem with the Application.DoEvents()-call, but I need that so I can press the button.

Also, if you notice anything else in my code that I could do better, please let me know, I'm not very experienced at coding, so any help and constructive criticism is welcome. :-)

Thank You!

Benjamin

Are you calling this function from a click event on the same button? — krillgar
– krillgar, Commented Dec 22, 2016 at 14:56
It sounds to me like you're breaking out of these for loops somehow and starting over. It's hard to say what the problem is without the rest of the code. — EJC
– EJC, Commented Dec 22, 2016 at 15:00
j = 0; j < items.Count() - 1 - i; j++ this line here doesn't pass the smell test. why would you subtract i here? — Muckeypuck
– Muckeypuck, Commented Dec 22, 2016 at 15:12
krillgar: I'm stupid. Yes I do, so the function gets called again when I want to continue. Thanks! — tambenj
– tambenj, Commented Dec 23, 2016 at 8:15

Master117 · Accepted Answer · 2016-12-22 14:57:08Z

2

You don't create i and j in the for-loops, i and j might get changed somewhere else in your app. Try this:

for (int i = 0; i < items.Count(); i++)
{
    for (int j = 0; j < items.Count() - 1 - i; j++)
    {
        //lbl_i.Text = Convert.ToString(i);
        //lbl_j.Text = Convert.ToString(j);

        if (items[j] > items[j + 1])
        {
            swap(j, j + 1); //swaps the items at two given indecies
            draw(); // draws the array to the picturebox
        }

        while (sorting == false) //the sorting is paused
        {
            Application.DoEvents();
        }
    }
}

The change is in: int i, int j

answered Dec 22, 2016 at 14:57

Master117

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1 Comment

tambenj Over a year ago

I had it like this at first, and it didn't work either. int i and int j are initialised right before the two loops.

tambenj · Accepted Answer · 2016-12-23 08:28:44Z

Found the answer: The problem was, that I was calling this function from the same button in the first place. In its click-event, I have an if-statement to check if the button said "Pause" or "Start", but when i paused the programm, it said "Start" again. So when I click it, the function gets called again and int i and int j are reinitialised to 0.

Code in the click-event:

    private void btn_start_Click(object sender, EventArgs e)
    {
        //new added code
        if (btn_start.Text == "Start")
        {
            btn_start.Text = "Pause";
            sorting = true;
            sort();
        }
        else if (btn_start.Text == "Pause")
        {
            btn_start.Text = "Continue"; // '= "Start"' in the old code
            tmr_sorting.Stop();
            sorting = false;
        } 
        // new added code
        else if (btn_start.Text == "Continue")
        {
            btn_start.Text = "Pause";
            sorting = true;
        }
    }

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