Why is double x * double x not equal to int y

Question

I am into this code but I need an explanation as to why

            int n = 6;
            int count = 0;
            double end = Math.Sqrt(n);
            for (int i = 1; i < end; i++)
            {
                if (n % i == 0)
                    count += 2;
            }
            Console.WriteLine(end * end + " - " + n);
            Console.WriteLine(end * end == n);
            if (end * end == 6)  
                Console.WriteLine("why");

returns false in the second Console.Writeline but if n=9 returns true

Comparing floating point values for equality doesn't work that way. See https://learn.microsoft.com/de-de/dotnet/api/system.double.equals?view=netframework-4.8 and https://stackoverflow.com/questions/3874627/floating-point-comparison-functions-for-c-sharp — Markus Deibel, Jul 24 '19 at 10:34
@AFriend the first `Console.Writeline` shows the value of `end * end` together with `n` — CodeRed, Jul 24 '19 at 10:36
Mostly likely a fitting duplicate https://stackoverflow.com/questions/1420752/is-double-multiplication-broken-in-net) similar questions are asked every couple of days — TheGeneral, Jul 24 '19 at 10:37
[Fiddling](https://dotnetfiddle.net/8a59Gl) around your example, try with `9`.. — Sinatr, Jul 24 '19 at 11:28

score 0 · Answer 1 · answered Jul 24 '19 at 10:35

0

end is a double and is equal to the square root of 6. Even though end * end is supposed to be 6, you are comparing double to int with the = sign which is a big no-no.
In this answer you can see the correct way to do so.

answered Jul 24 '19 at 10:35

pappbence96

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Yea, I know I am comparing double to int but how come if I use `n = 9` it will return `true`? – CodeRed Jul 24 '19 at 10:40

Why is double x * double x not equal to int y

1 Answers1