C# - string to number

Question

Again i come back with one of my problems and queries.

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

namespace compare_string
   {
     class Program
     {
        static void Main(string[] args)
        {
            string str1 = "85.8500000000000";
            string str2 = "85.85";
            double num1 = Convert.ToDouble(str1);
            double num2 = Convert.ToDouble(str2);
            if (num1 != num2)
            {
                 Console.WriteLine("Unequal");
            }
            else {
                 Console.WriteLine("Equal");
            }
             Console.ReadKey();
         }
    }
  }

Why is give that the two numbers are unequal? Thanks in advance!

@κωστας Σοφός Are you sure, is the "." your system decimal separator? — Hamlet Hakobyan
– Hamlet Hakobyan, Commented Nov 20, 2012 at 13:22
also, try to avoid comparations between floating point numbers, since they tend to be a problem usually, see here: stackoverflow.com/questions/1398753/… — fnurglewitz
– fnurglewitz, Commented Nov 20, 2012 at 13:25
@tr3 What's the use of numbers if you're not allowed to compare them? Do you know of an application? — Jeppe Stig Nielsen
– Jeppe Stig Nielsen, Commented Nov 20, 2012 at 13:32
@JeppeStigNielsen I believe he meant to compare equality between floats. It's better to see if the difference between floats is in a specified range than to be exact equality. — Ichabod Clay
– Ichabod Clay, Commented Nov 20, 2012 at 13:48

L.B · Accepted Answer · 2012-11-20 13:19:20Z

12

This is most probably related with your locale. Try this, it should work

double num1 = Convert.ToDouble(str1,CultureInfo.InvariantCulture);
double num2 = Convert.ToDouble(str2,CultureInfo.InvariantCulture);

Alo try printing your numbers, you will see the difference.

answered Nov 20, 2012 at 13:19

L.B

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3 Comments

amigo Over a year ago

I should use a library i.e using **** to have access to CultureInfo.***

L.B Over a year ago

It is in System.Globalization

amigo Over a year ago

Thanks. It is working. I read this values from csv files and i want to compare these. Thanks again

Daniel Hilgarth · Accepted Answer · 2012-11-20 13:20:12Z

5

The reason is that you are running it on a machine that uses the comma as decimal character, not the dot. When you change your code to the following, it will print Equal.

string str1 = "85,8500000000000";
string str2 = "85,85";

This again shows why you always should specify a culture in methods like this. Your original code will work with dots when you specify CultureInfo.InvariantCulture:

string str1 = "85.8500000000000";
string str2 = "85.85";
double num1 = Convert.ToDouble(str1, CultureInfo.InvariantCulture);
double num2 = Convert.ToDouble(str2, CultureInfo.InvariantCulture);

CultureInfo is in the namespace System.Globalization.

answered Nov 20, 2012 at 13:20

Daniel Hilgarth

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1 Comment

amigo Over a year ago

Thanks a lot my friend. I have dot because i read these values from csv files. Thank you again for your advise

fero · Accepted Answer · 2012-11-20 13:19:31Z

1

I think it is because of your current locale. Did you ever look into these values?

For me in Germany, the first number is 858500000000000, the second is 8585.

answered Nov 20, 2012 at 13:19

fero

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Comments

Jeppe Stig Nielsen · Accepted Answer · 2012-11-20 13:20:37Z

0

A guess would be that the CurrentCulture of your thread has a NumberFormatInfo where the NumberDecimalSeparator is not ".".

If you use Convert.ToDouble(str1, System.Globaliztion.CultureInfo.InvariantCulture) the local culture of your thread will be disregarded.

answered Nov 20, 2012 at 13:20

Jeppe Stig Nielsen

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