Convert a string in a label to int not working properly

Question

I have the following code:

int a = Int32.Parse(weight.Text);
double b = 0;

if (this.wcf.SelectedItem == weighing)
{
    b = (a * 1.03) / 1000;
    wll.Content = b.ToString();
}

weight is the name of a TextBox and in this TextBox where the input is made which is 50000. wll is a Label where the calculation of b is shown. wll shows 51.5 which is correct.

I want to use the value of b in a calculation further down and therefore I have defined a new int:

int p = Convert.ToInt32(b);
double g = 0;          

double sq = Math.Sqrt(50 / p);

The value of sq should then be 0,985 and is shown in the label daf, but the program shows 1,492. Something is not correct here, can anyone help me?

g = (1.09 + (0.41 * sq));
daf.Content = g.ToString();

Be careful with integer divisions. You should use doubles IE 50.0 not 50 — Steve, Jan 28 '16 at 11:45
@Ian I will try to investigate and see if I can find any mistakes. But the conversion of the value in the label to an int is done correctly? — Thomas Eikje Gjerde, Jan 28 '16 at 11:59
@ThomasEikjeGjerde if your `weight.Text` is of the form `50000` or `5000` or `111111`. Then it is ok. ;) but let say it is of the form `12.131`, or `156.41`, or `50.1213`, then it is *not* ok. Basically, you need to find parser which suits with your `string` format. ;) — Ian, Jan 28 '16 at 12:01

Ian · Accepted Answer · 2016-01-28T11:56:54.900

1

Beware of this:

int p = Convert.ToInt32(b);
double g = 0;          
double sq = Math.Sqrt(50 / p); //int/int

this will make you have Math.Sqrt(int), losing precision. Instead, you should do:

double sq = Math.Sqrt(50D / p); //double/int

or

double sq = Math.Sqrt((double)50 / p); //double/int

or

double sq = Math.Sqrt(50.0 / p); //double/int

Declare 50 as double

In addition, since your b can have result of non-integer, you may want to change this line too:

int p = Convert.ToInt32(b); //same issue losing precision

into

double p = Convert.ToDouble(b); //use double instead

edited Jan 28 '16 at 11:56

answered Jan 28 '16 at 11:46

Ian

30,182
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I declared 50 as a double both with and without decimals. That didn't change anything unfortunately. – Thomas Eikje Gjerde Jan 28 '16 at 11:54
Thanks for your help, the convertion to a double a helped! – Thomas Eikje Gjerde Jan 28 '16 at 12:07
@ThomasEikjeGjerde great! That being the real culprit then... ;) – Ian Jan 28 '16 at 12:12

score 0 · Answer 2 · answered Jan 28 '16 at 11:57

0

One of the main thing that i can see is that in your code you have used

int p = Convert.ToInt32(b);

this will make p = 51 and not 51.1

your code should work fine if you make p as double, and convert to double

double p = Convert.ToDouble(b)

answered Jan 28 '16 at 11:57

abhinav

31
4

Thanks for your help, the convertion to a double a helped! – Thomas Eikje Gjerde Jan 28 '16 at 12:07
You are welcome. Always keep an eye on what precision you are working on and what datatype you are using. – abhinav Jan 28 '16 at 14:14

score 0 · Answer 3 · answered Jan 28 '16 at 12:00

First, you are converting b into an int. so you're losing the 0.5 precision, becoming 51, not 51.5. Change your p into a double and don't convert b! that will give you sq as 0,985. Then you are printing out g, not sq. that's why the program is showing 1,492, not 0,985:

daf.Content = sq.ToString();

Convert a string in a label to int not working properly

3 Answers3