Mine

void Ball::snap(double precision)
{
    double prev, next;
    double x_matissa, y_matissa;
    x_matissa = x - floor(x);
    y_matissa = y - floor(y);
    for (next = 0; next < x_matissa; next += precision)
        prev = next;
    x = floor(x) + ((x_matissa > (prev + precision / 2)) ? next : prev);
    prev = 0;
    for (next = 0; next < y_matissa; next += precision)
        prev = next;
    y = floor(y) + ((y_matissa > (prev + precision / 2)) ? next : prev);
}