Hi, i have a question, i wondering what sequent line do:

index %= 49; // limit the "index" value

Whether it's equal to:

if(index == 49)index = 0;

?

I want to understand what %= realy does

the % operator limits the value ( in this case index) to a maximum of 49, so that its impossible to go 50,51 etc.

something similar would be:
if(index > 100) { index = 0; )

but this is bad because it doesn't consider the actual index value, it just sets it to 0.

instead index %= 49 is just an abbreviation for:
index = index % 49;

and the % means just this:
remainder of index / 49
so with % Acknex returns an integer remainder of 2 numbers

It mean the limit of the variable.

The modulo (%) operator finds the remainder of the division of a number by another. As an example, 7 % 3 = 1, 8 % 4 = 0 and so on.
index %= 49 makes sure that index can't exceed 48; it will be set to 0, 1, 2, ..., 47, 48, 0, 1, 2... as index is incremented.

I get it. I count first 3 values and get that circle i just think now, why i don't count it before, cause i know what is modulo... but thanks for reply