How to compare double?

Question

1.00/5 (1 vote)

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The next code doesn't show the message "Equal" when x is equal 1:

C#

for (double x = 0; x <= Convert.ToDouble(1); x += 0.1)
{
    MessageBox.Show(x.ToString());
    if (x == Convert.ToDouble(1)) MessageBox.Show("Equal");
}

How to fix?

Posted 12-Oct-14 2:19am

Ziya1995

Updated 12-Oct-14 2:20am

v2

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Comments

[no name] 12-Oct-14 8:26am

http://msdn.microsoft.com/en-us/library/ya2zha7s(v=vs.110).aspx

Afzaal Ahmad Zeeshan 12-Oct-14 8:33am

Exactly, in that case both the operands are of double type. The precision causes the types to be not equal to an integral value.

For more, see my answer and the fiddle that evaluates your values.

[no name] 12-Oct-14 8:38am

No thanks. I would prefer code that works. Nice try though.

Afzaal Ahmad Zeeshan 12-Oct-14 8:47am

I am sorry, the last paragraph was for the OP, not for you.

However, that code works try the fiddle, and if you meant you wanted a .NET way of doing it, then yeah! You're right. :-)

Afzaal Ahmad Zeeshan 12-Oct-14 8:51am

Sorry, I read the second solution after I posted the comment!

2 solutions

Solution 4

After you read the article Carlo posted - and understood the floating point problem...
Use Decimal[^]...

C#

for ( decimal x = 0; x <= ( decimal )1; x += ( decimal )0.1 )
{
    Debug.WriteLine ( x.ToString ( ) );
    if ( x == ( decimal )1 )
        Debug.WriteLine ( "Equal" );
}

Posted 13-Apr-15 9:44am

Kornfeld Eliyahu Peter

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CPallini · Accepted Answer · 2015-04-13T09:15:00

Solution 3

Obligatory link: "What Every Computer Scientist Should Know About Floating-Point Arithmetic"[^].

Posted 13-Apr-15 9:15am

CPallini