Casting double to int

  • Thread starter Thread starter Barry
  • Start date Start date
B

Barry

What is the best way to round a double and store it in an int (C#)?
I'm currently using
intVar = (int)Math.Round(doubleVar);
I'm worried that the return value of e.g. Math.Round(2.1) might be
1.99999999999999999999999 (due to quirks of binary/decimal conversion),
and (int) will then truncate it to 2.
 
You could use:

int number = (int)Math.Ceiling(doubleValue);

The smallest whole number greater than or equal to doubleValue.

int number = Convert.ToInt32(doubleValue);

rounds it to the nearest number.
 
I'm worried that the return value of e.g. Math.Round(2.1) might be
and (int) will then truncate it to 2.
Click to expand...

Doesn't 2.1 round to 2 ?

How about:

int i = (int) (d+0.5)

Are you testing against a bunch of samples and seeing erroneous results? Or
are you perhaps worrying needlessly?
 
ints are *exactly* representable as double, and longs are too when smaller
than 2^52 in absolute value.

So, Math.Round(someDecimal) will never be something like
someInt.99999999999999999999, it will be exactly someInt.000000000000000 and
the cast will always give the correct result.

But this is a special case, and most decimal numbers are *not* exactly
representable as doubles. So, you are right to be careful about this.

Bruno.
 
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