How can I modulo when my numbers start from 1, not zero? -

I think this solution is quite simple, but I was thinking about this for a while and did not come With elegant solution.

I have many numbers, such as 1..10 = (1,2,3,4,5,6,7,8,9,10) , which is the circular , Which means that for the first time after the last one ( Next (10) = 1 ).

For a given number, i & gt; In the category, I want to do the next M -th, and the previous M -common like Next (5,1) = 6 Next (10,1) = 1 Next (10,2) = 2 prev (5,2) = 3 Previous (1,1) = 10 prev (1,2) = 9 .

For Next I can simply take (i + m)% n where n is the length of the border ( n = 10 in the example) but I could not find a great solution for previous .

Simply subtract 1 and add 1 later.

In most programming languages, you need to search the "previous" value, because for the negative number, the modules do not work in this case as you want: this negative number.

Here is the C / C ++ version:

  int next (int i, int m, int n) {return (i + m - 1)% n + 1; } Int prev (int i, int m, int n) {return (i - m + n - 1)% n + 1; }  

However, Perl always gives a positive value in modulo (at least when the second operator is a positive integer). Basically, if you want it, you can write the following and + $ _ [2] :

  sub nxt {($ _ [0] + $ _ [1] - 1)% $ _ [2] + 1; } Sub PRV {($ _ [0] - $ _ [1] - 1)% $ _ [2] + 1; }