C: Integer Division Rounding

hydraMax · 03-08-2012, 10:38 AM

Sanity check: In C, integer division does always round down, correct? 15/4 produces 3 on any architecture, yes?

Doc CPU · 03-08-2012, 10:56 AM

Hi there,

Quote:

Originally Posted by hydraMax

Sanity check: In C, integer division does always round down, correct? 15/4 produces 3 on any architecture, yes?

if you want to call it "rounding", yes.
That's how integer division is defined: 15 / 4 is 3, with a remainder of 3.
Or: "How often does 4 fit entirely into 15?"

[X] Doc CPU

sundialsvcs · 03-08-2012, 01:59 PM

Math operations never round anything ... unless you do it yourself by calling an appropriate rounding function. Integer division always truncates.

jlinkels · 03-08-2012, 02:42 PM

Wow this has been a long time since I programmed C... forgot even what is allowed.

Code:

int i;
i = 15/4;

apparently assigns 3 to i.

What will this do:

Code:

int i;
i = 15.0/4.0;

Will the compiler call the correct conversion?

jlinkels

tuxdev · 03-08-2012, 05:02 PM

It'll truncate when the implicit cast happens, 'i' will still be 3

orgcandman · 03-09-2012, 10:11 AM

Quote:

Originally Posted by tuxdev

It'll truncate when the implicit cast happens, 'i' will still be 3

Indeed, that's actually specified in the standard, so you can rely on this behavior*.

*= there are a few caveats, so be sure to read the c99 standard very thoroughly w.r.t. arithematic and conversion.