Question

I’m wondering what int id = 5%2; does exactly and also look for similar things.

Reason:

I want to calculate by a number on which row / column the item should be standing.

[Example]

I have a grid which is 5×5.

If id = 05, it should be on the 1st row and the 5th column

If id = 10, it should be on the 2nd row and the 5th column

If id = 12, it should be on the 3rd row and the 2nd column

How you catch my drift!

(ps: feel free to edit my tags. Not sure what to put on this question)

Answer 1

The modulus (% in some C-derivative languages) is the remainder left over when one number is divided by another. So 38 % 6 is 2 (38 / 6 is 6 with a remainder of 2).

It’s typically used for exactly the sort of thing you’re asking about. If your 5×5 grid is:

    col  1  2  3  4  5
row
 1       1  2  3  4  5
 2       6  7  8  9 10
 3      11 12 13 14 15
 4      16 17 18 19 20
 5      21 22 23 24 25

then the row can be calculated as (x-1)/5+1 (that’s integer division rather than floating point) and the column as (x-1)%5+1:

 x   (x-1)/5+1   (x-1)%5+1
--   ---------   ---------
 5       1           5
10       2           5
12       3           2

The reason you initially subtract the one and then add it on is because modulus works best on zero-based numbers while yours are one-based. The subtract/add is to turn your scheme into zero-based before performing the modulus, then turning it back into one-based afterwards.