Modulo

Division (this is NOT modulo)Modulo
7 / 3 = 27 % 3 = 1
6 / 4 = 16 % 4 = 2
-8 / 3 = -2-8 % 3 = -2
21 / 7 = 321 % 7 = 0
1 / 5 = 01 % 5 = 1

The modulo operator looks like this:

//It's this guy below
%

It is used to get the remainder of division:

 
//The value of x after the code below runs is 0
//because 3 divides 3 evenly
x = 3 % 3
 
//The value of x after the code below runs is 1
//because 4/3 gives a remainder of 1
x = 4 % 3
 
//The value of x after the code below runs is 2
//because 5/3 gives a remainder of 2
x = 5 % 3
 
//The value of x after the code below runs is 0
//because 3 divides 6 evenly
x = 6 % 3
 
//The value of x after the code below runs is 1
//because 7/3 gives a remainder of 1
x = 7 % 3

You seeing the pattern here? The pattern for anything modulo 3 is to cycle through 0, 1, and 2. There are 3 different possible answers, starting at 0 and going to 2.

This same pattern exists for any positive integer number. For example, anything modulo 5 will cycle through the numbers 0 to 4:

 
//0
z = 25 % 5
 
//1
z = 26 % 5
 
//2
z = 27 % 5
 
//3
z = 28 % 5
 
//4
z = 29 % 5
 
//0
z = 30 % 5