Round to nearest multiple of a number

Question

Is there an idiomatic way to round to the nearest multiple of a number, short of rounding both up and down and seeing which one is closest?

Assume only integers:

number   multiple   result
12       5          10
13       5          15
149      10         150

Answer 1

Add half of the multiple, then round down.

result = ((number + multiple/2) / multiple) * multiple;

or

result = number + multiple/2;
result -= result % multiple;

This rounds up if the number is exactly in the middle. You might need to tweak the calculation if you want different behaviour in that case. Also, beware overflow if number might be near the top of the type's range.

Answer 2

Easy Java Solution:

public Long roundToNearestLong(Long number, Long multiple) {
        if (number == null)
            return 0L;

        Long smallerMultiple = (number / multiple) * multiple;
        Long largerMultiple = smallerMultiple + multiple;

        // Return of closest of two
        return (number - smallerMultiple >= largerMultiple - number) ? largerMultiple : smallerMultiple;
    }

Answer 3

Mike Seymour的答案假设“数字”为正

Answer 4

I've answered this before on Rounding off a number to the next nearest multiple of 5

With using cmath::abs

int rounded = n + abs((n % denom) - denom);

You can change denom with any denomination you want