Learning Processing: A Beginner's Guide to Programming Images ...

202 Learning Processing
And most recently, in Chapter 10, we tested intersection using the Pythagorean Th eorem.
float d = dist(x1,x2,y1,y2);
Th ese are just a few examples we have seen so far and as you get more and more advanced, you may even
fi nd yourself online, late at night, googling “ Sinusoidal Spiral Inverse Curve. ” For now, we will start with a
selection of useful mathematical topics.
13.2
Modulus
We begin with a discussion of the modulo operator , written as a percent sign, in Processing. Modulus is a
very simple concept (one that you learned without referring to it by name when you fi rst studied division)
that is incredibly useful for keeping a number within a certain boundary (a shape on the screen, an index
value within the range of an array, etc.) Th e modulo operator calculates the remainder when one number
is divided by another. It works with both integers and fl oats.
20 divided by 6 equals 3 remainder 2. (In other words: 6*3 � 2 � 18 � 2 � 20.)
therefore:
20 modulo 6 equals 2 or 20 % 6 � 2
Here are a few more, with some blanks for you to fi ll in.
17 divided by 4 equals 4 remainder 1 17 % 4 � 1
3 divided by 5 equals 0 remainder 3 3 % 5 � 3
10 divided by 3.75 equals 2 remainder 2.5
10.0 % 3.75 � 2.5
100 divided by 50 equals ___________ remainder ______ _________ 100 % 40 � ____________
9.25 divided by 0.5 equals ___________ remainder _______________ 9.25 % 0.5 � ______ _____
You will notice that if A � B % C , A can never be larger than C . Th e remainder can never be larger than
the divisor.
0 % 3 � 0
1 % 3 � 1
2 % 3 � 2
3 % 3 � 0
4 % 3 � 1
etc .