Processing: Creative Coding and Computational Art

Assignment operators
The only other operators you need to look at for now are used for assignment operations.
The simplest assignment operation just uses the = operator. For example, to assign the
value 55 to the int variable speed, you’d simply write the following:
int speed = 55;
Again, the = sign is used for assignment, not equality. When you test for equality in
Processing and Java, instead of writing if(speed=55), you need to write if(speed==55).
The first way actually assigns the value 55 to speed; the second way tests if speed is actually
equal to 55. Using the single-equal sign when testing for equality is a very common
mistake new coders make. We’ve been conditioned to think of equality as =, not ==, so it
makes sense that new coders find it confusing.
When I write an assignment statement, for example
x = 4;
I am assigning 4 to x. So now the value of x evaluates to 4. Let’s say I want to add 3 to x—
I could write x + 3, right? Let’s try it.
Write the following two lines of code in Processing and click run.
int x = 4;
x + 3;
Surprised you got an assignment error? It’s because you’re adding 3 to x, but not assigning
the solution anywhere. Remember that computers are really dumb. If they can’t put the
value anywhere, they don’t know what to do. Fortunately, the Processing compiler sends
out a compiler error letting you know this.
You can fix the preceding assignment in a couple of ways—but the easiest way to add 3 to
x, and then assign the value back to x, is as follows:
x = x + 3;
Now this may look a little odd, having something assigned to itself. But reading the expression
in English helps: add the value of x and 3 and then assign that value to x. Assignment
operations happen from right to left. It may take a little time playing with this to get it
clear in your brain. These operations work the same way for the other mathematical operators
as well. Here’s a division example:
float y = 10.4;
// divide by 1.25
y = y / 1.25;
CODE GRAMMAR 101
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