Re: Dumb Question - Casting

Daniel Egeberg wrote: > On Thu, Feb 18, 2010 at 16:47, Chuck <chuck.carson@gmail.com> wrote: >> Sorry, been doing heavy perl and haven't written any PHP in 3 years so a tad >> rusty. >> >> Can someone explain why the second expression in this code snippet evaluates >> to 7 and not 8? >> >> $a = (int) (0.1 +0.7); >> >> echo "$a\n"; >> >> $x = (int) ((0.1 + 0.7) * 10); >> >> echo "$x\n"; >> >> $y = (int) (8); >> >> echo "$y\n"; >> > > The reason why you get 7 instead of 8 is because you are using > floating point arithmetic. 0.1 (i.e. the fraction 1/10) does not have > a finite representation in base 2 (like you cannot finitely represent > 1/3 in base 10). So the number 0.1 is represented in the computer as a > number that is strictly less than 0.1 so when you do 0.1+0.7=x then > you have x<0.8 in the computer (think 7.9999999...). When you cast to > int you just truncate the number, i.e. you chop off the fractional > part leaving you with 7. > yup as Daniel pointed out; this is correct - love floats & casting! see: $y = ((0.1 + 0.7) * 10); $x = (int)$y; $z = intval($y); var_dump($y); var_dump(serialize($y)); var_dump($x); var_dump($z); outputs: float(8) string(55) "d:7.99999999999999911182158029987476766109466552734375;" int(7) int(7) lovely! - note: serializing gives us the exact value of the float regards, Nathan