Why?

[Mark W]

Why does this evaluate to 7?

 

echo (int) ((0.1 + 0.7) * 10); 

 

I was told it is because (0.1 + 0.7) * 10) is being stored as 7.99999999, and everything after the decimal is cut off by the conversion to int, but why is it being stored as that? Surely ((0.1 + 0.7) * 10) should be being stored as 8 even before the data type conversion?

[.josh]

some kind of bug?

 

echo (int) ((0.1 + 0.7) * 10); // output: 7

echo (int) ((.1 + .7) * 10); // output: 7

echo (int) ((1.1 + 0.7) * 10); // output: 18

echo (int) ((0.1 + 1.7) * 10); // output: 18

echo (int) ((1.1 + .7) * 10); // output: 18

echo (int) ((.1 + 1.7) * 10); // output: 18

echo (int) (10 * (0.1 + 0.7));  // output: 7

echo (int) 10 * (0.1 + 0.7); // output: 8

 

seems to be casting the first number as int and then operating.

[rhodesa]

we are here again?

 

read

http://www.phpfreaks.com/forums/index.php/topic,231460.msg1073336.html#msg1073336

[PFMaBiSmAd]

Must be a class assignment to see if they can find out how computers do (or don't do) floating point math.

[rhodesa]

Must be a class assignment to see if they can find out how computers do (or don't do) floating point math.

 

good call. cus the equation is STRAIGHT off the PHP website

[.josh]

haha yeah I noticed that, too, when I followed the link trail.  I even learned a thing or two.