Getting a value of 0 when dividing 2 longs in c#

Question

I am trying to divide the values of DriveInfo.AvailableFreeSpace & DriveInfo.TotalSize to try and get a percentage of it to use in a progress bar.

I need the end value to be an int as progressbar.value requires an int and the above methods return a long.

I have this as the values:

164660715520---AvailableFreeSpace

256058060800---TotalSize

When I try and set the progressbar.value using this method I also get an error:

progressBar1.Value=(int)(dInfo.AvailableFreeSpace/dInfo.TotalSize)*100;

When I use this code to try and get a value it just returns a 0.

label10.Text =  (((int)dInfo.AvailableFreeSpace/dInfo.TotalSize)*100).ToString();

I've even tried this and it doesn't work:

label10.Text = ((dInfo.AvailableFreeSpace/dInfo.TotalSize)*100).ToString();

I know I still have to do some formatting to get it to look good but whenever I run the code it just returns a 0.

Could it have something to do with the conversion from long to int?

The value of 164660715520/256058060800 is 0.64. That's why you're getting 0 I would imagine. — Jamie Dixon, Sep 23 '12 at 14:07

Tudor · Accepted Answer · 2012-09-23T14:36:24.090

27

Integer division returns only the integer part. So 3/5 will be 0. You'll need to treat at least one of the factors as a floating point number. Try this:

label10.Text =  (((int)((double)dInfo.AvailableFreeSpace/dInfo.TotalSize)*100)).ToString();

edited Sep 23 '12 at 14:36

answered Sep 23 '12 at 14:08

Tudor

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Now would I be able to just cast that into an int to get a whole number? – Zeratas Sep 23 '12 at 14:11
@Sempus if you only want the integer part, you can `*100` first. – Dante May Code Sep 23 '12 at 14:13
1

In some cases, double is not big enough to cover long – cuongle Sep 23 '12 at 14:14
decimal type is larger than than long which use 128 bit, double just use 64 bit, same with long – cuongle Sep 23 '12 at 14:16
@Sempus: Ahh I get what you mean. Sure you can, just cast the final result to `int`. – Tudor Sep 23 '12 at 14:16
@Cuong Le: I agree, but I doubt the amount of free space will exceed the max value of double. – Tudor Sep 23 '12 at 14:18
Yea, I really only care about the whole number part(int) so the decimal part I really don't care about. Just getting percentages. – Zeratas Sep 23 '12 at 14:22

score 16 · Answer 2 · answered Sep 23 '12 at 14:09

The first way with casting dInfo.AvailableFreeSpace to int right away is not going to work, because the number 164660715520 that you are trying to cast does not fit in 32 bits. You need to stay in 64 bits as long as you can.

The trick to avoiding floating-point arithmetics is to multiply by 100 first, and then do the division.

As long as the number times 100 is within the allowed size (and in your case, it is) the result has a good precision:

label10.Text = ((100*dInfo.AvailableFreeSpace/dInfo.TotalSize)).ToString();

Demo on ideone (prints 64).

long total = 256058060800L;
long avail = 164660715520L;
var pct = (100*avail/total).ToString();
Console.WriteLine("{0}", pct); // 64

score 5 · Answer 3 · edited Jan 07 '14 at 15:18

The value is rounding down to 0, as long types cannot have decimal places, only whole integers.

Cast as a decimal type before multiplying by 100

For Example (In my case where I am calculating progress percentage for ProgressBar):

double someVariable = (double)longVariable1 / (double)longVariable2;

Code is given below:

public partial class Form1 : Form
{
   public Form1()
    {
         web.ProgressChanged += new WebBrowserProgressChangedEventHandler(web_ProgressChanged);
    }

private void web_ProgressChanged(object sender, WebBrowserProgressChangedEventArgs e)
    {

        <strong>double t = (100 * (double)e.CurrentProgress / (double)e.MaximumProgress);</strong>
        if (t < 0)
            return;
        int c = (int)t;
        progressBar.Value = c;

        if (c == 100)
        {
            label1.Text = "Done";                
        }
    }
}

score 1 · Answer 4 · answered Sep 23 '12 at 14:13

1

make your dInfo.AvailableFreeSpace and dInfo.TotalSize decimal or double type to avoid casts Or

uselabel10.Text = (((double)dInfo.AvailableFreeSpace/dInfo.TotalSize)*100).ToString();

answered Sep 23 '12 at 14:13

DSharper

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score 0 · Answer 5 · answered Dec 27 '17 at 21:46

I might be a bit late but I had this issue when trying to compare timespan's. Eventually I cast each timepsan to a string and manually computed the ratio

    private static double Improvement(string efficientTime, string inefficientTime)
    {
        var magnitude = Math.Pow(10, (inefficientTime.Length - efficientTime.Length));
        var time2 = (double) Convert.ToInt32(efficientTime.Substring(0, 5));
        var time1 = (double) Convert.ToInt32(inefficientTime.Substring(0, 5));
        var sigRatio = (time2 / time1);

        var sigPercent = sigRatio * magnitude;

        var improvement = sigPercent;
        return improvement;
    }

Getting a value of 0 when dividing 2 longs in c#

5 Answers5