====== mod ======
{{tag>math}}
''num mod(num a, num b)''

[[:types|num - any numeric type (int or fixed)]]

===== Description =====
This function implements modulo division ''a % b'', but, unlike the ACS operator, it handles negative values of ''a'' like mathematical modulo, making ''a'' cycle around on the range ''[0, b)''.

This makes its result safe to use an array index, as the result is not negative for negative values of ''a''. 

Only positive values of ''b'' are supported.

===== Examples =====
<code>
mod(-5, 3) -> 1
mod(-4, 3) -> 2
mod(-3, 3) -> 0
mod(-2, 3) -> 1
mod(-1, 3) -> 2
mod(0, 3) -> 0
mod(1, 3) -> 1
mod(2, 3) -> 2
mod(3, 3) -> 0
mod(4, 3) -> 1
mod(5, 3) -> 2
</code>

Using mod to implement menu cycling easily:

<code>
if (KeyPressed(BT_DOWN))
    menuindex++;
if (KeyPressed(BT_UP))
    menuindex--;
    
menuindex = mod(menuindex, NUM_MENU_ITEMS);
</code>