c++ - Find closest number from uniform grid -

I have an integer positive number n . For example, suppose that n = 5 if we look at the polygon of n , we look at these numbers (let's call it an N-grid) [ ... -15, -10, -5, 0, 5, 10, 15, ...] Now I need to write a function F (n, n) , which is given an integer N , showing the closest number from that n-grid. For, F (n, 0) = 0 (for any N). F (5, 4) = 5 , F (5, 7) = 5 , F (5, 8) = 10 , F (5, -13) = -15 and so on.

I have written this function:

  int constx = ((:: stomach (n) + (n / 2)) / n) * n; If (N> gt; {return x; } Other {return -x; }   
 It seems like it does not like how it looks at work. Can anybody suggest improvement?   
 
 
 You can remove from  if   (n / abs ( N))  By multiplying x by and without saving it in  x , the value calculated also immeadiatelly.  
 I do not do this, because it will damage readability.