I was curious to know how I can round a number to the nearest tenth whole number. For instance, if I had:
int a = 59 / 4;
which would be 14.75 calculated in floating point; how can I store the number as 15 in "a"?
views:
686answers:
3
+8
A:
The standard idiom for integer rounding up is:
int a = (59 + (4 - 1)) / 4;
You add the divisor minus one to the dividend.
Jonathan Leffler
2010-03-11 05:23:18
What if you want to perform a mathematical round (14.75 to 15, 14.25 to 14)?
Chris Lutz
2010-03-11 05:24:35
Ugh...then you have to think...add (n - 1) / 2, more or less. For n == 4, you want x % n ∈ { 0, 1 } to round down, and x % n ∈ { 2, 3 } to round up. So, you need to add 2, which is n / 2. For n == 5, you want x % n ∈ { 0, 1, 2 } to round down, and x % n ∈ { 3, 4 } to round up, so you need to add 2 again...hence: `int i = (x + (n / 2)) / n;`?
Jonathan Leffler
2010-03-11 05:32:30
+4
A:
int a = 59.0f / 4.0f + 0.5f;
This only works when assigning to an int as it discards anything after the '.'
0xC0DEFACE
2010-03-11 05:23:22
Note that this is FLOATING pointer solution. I recommend that you use integer operation for many reasons.
Yousf
2010-03-11 11:32:24
What problems? I've used this before and have never encountered a problem.
0xC0DEFACE
2010-03-12 01:05:13
+3
A:
As written, you're performing integer arithmetic, which automatically just truncates any decimal results. To perform floating point arithmetic, either change the constants to be floating point values:
int a = round(59.0 / 4);
Or cast them to a float or other floating point type:
int a = round((float)59 / 4);
Either way, you need to do the final rounding with the round() function in the math.h header, so be sure to #include <math.h>.
Chris Lutz
2010-03-11 05:24:42