数字降序C＃

Question

I was able to write this tiny segment of this program to display the numbers in Ascending order but i still cant get it to display it in Descending order.

Basics of what this program should do is takes in two number values from the user in the form of "From" and "To" and displays it as a list in the listbox. The users choice of either ascending or descending order depends on which of the two Radio buttons he has selected.

    private void btnCalc_Click(object sender, EventArgs e)
    {

        double fromNum, toNum, total = 0;

        fromNum = double.Parse(txtFrom.Text);
        toNum = double.Parse(txtTo.Text);

        lstResult.Items.Clear();
        lblResult.Text = "";

        if (radAsc.Checked)
        {
            while (fromNum <= toNum)
            {
                lstResult.Items.Add(fromNum);

                total = total + fromNum;

                fromNum++;
            }
        }

        else
        {
            while (fromNum >= toNum)
            {
                lstResult.Items.Add(fromNum);

                total = total + toNum;

                toNum--;
            }
        }

        lblResult.Text = total.ToString();
    }

Here's an image to what the program looks like. http://imgur.com/SVwN3Tx

Note:- I am completely new to C# and I've just started taking it in College.

Answer 1

I suggest using for loop instead of while which makes the code easy to implement:

    if (radAsc.Checked)
    {
        // num += 1: - I've seen odds/even switch on the screenshot
        // so you may want to change/add num += 1 into num += 2
        for (double num = fromNum; num <= toNum; num += 1) {
          lstResult.Items.Add(num);
          total = total + num;
        }
    }
    else
    {
        // Descending order: 
        //   - start from the bottom (toNum)
        //   - loop until the top (fromNum) 
        //   - descend by 1 (num -= 1)
        for (double num = toNum; num >= fromNum; num -= 1) {
          lstResult.Items.Add(num);
          total = total + num;
        }
    }

Answer 2

You're decrementing the wrong value

while (fromNum >= toNum)
{
    lstResult.Items.Add(fromNum);

    total = total + toNum;
    toNum--;
}

So, here's what you're doing:

Say fromNum is 10, and toNum is 1.

After your first iteration, fromNum is still 10 but toNum is 0. Decrement the fromNum instead of toNum and it should work accordingly.

EDIT

Couple things to take note. If total is collecting the sum of all numbers, a neat way to write:

total = total + value;

is

total += value; .

You should also verify that the numbers will actually work before going into your logic. So if the radio button is selected for Ascending order, you want to make sure fromNum is less than toNum, and maybe throw up a message box if they're not:

if(fromNum < toNum)
    { run logic .... }
else
    { alert user ... }