Round to Next .05 in C

Question

Consider a float value like 1.82 set by the user. How do I find the next highest .05 value? For the given example the next highest value is 1.85.

Is the

Answer 1

Multiply by 20, use ceiling, divide by 20.

Answer 2

float fixedCeil(float num, float factor)
{
  float steps = 1.0f / factor;
  return ceil(steps*num)/steps;
}

assert(fixedCeil(2.43f, 0.05f) == 2.45f);

(assert is just fictional)

Answer 3

Code for @Justin's answer. Note that this is very easy to generalize.

#include <math.h>
#include <stdio.h>

int main(void) {
    int i;
    double numbers[] = {
        1.82, 0.3, 0.2, 0.5, 10000000000.849,
    };

    for (i = 0; i < sizeof(numbers)/sizeof(numbers[0]); ++i) {
        double scaled = ceil(20 * numbers[i]);
        printf("%.2f\n", scaled/20.0);
    }

    return 0;
}

Answer 4

You can use something like

    // Rounds X to the nearest Y
    double round(double x, double y)
    {
        return floor(x / y + 0.5) * y;
    }

Answer 5

A great useful and informative resource for Rounding methods.