A variable is something, that can take on different values at different times. In order to work with variables, we have to be familiar with different concepts.
Declaring a variable
In order for us to use a variable though, we first have to declare it. For example:
And voilà, we declared the variable int as x.
Initialising a variable
In the second step, we will initialise the variable by setting a value to it. For example:
int x = 10
x is now set to 10, and we can call
x throughout our sketch, and modify it.
Types of variables
In Processing there are multiple types variables that we can use in a sketch.
1. int variableS
int variable is used for integers, hence its name. Integers are whole numbers, such as 1, 2, 3, or 4. For example
int n = 100
2. Float variableS
The float, or floating points variable allows us to use values with decimals. For example
float e = 2.71828;
3. Boolean variableS
A boolean variable is a variable which is true or false. In Processing boolean variables are implied, i.e. they don’t need to be declared. For example
boolean switchVar = true;
Additional things we can do with boolean operators is inverting them by pre-pending an exclamation point prior to it. The exclamation point is a “not” operator. For example:
switchVar = !switchVar;
4. Char variables
Char stands for character. A character variable has a single letter or a number and it must be in single quotes. For example:
char charVar = 'V';
5. Byte variable
The byte variable is interesting in that sense that it is used in communication with serial ports such as Arduino. The byte variable has a range from -128 to 127.
byte dozen = 12;
6. Color variable
We can use the colour variable in such a way that we don’t have to remember the hex codes throughout our sketches, but instead refer to a colour’s name. For example:
color cherryBlossomPink = #FFB7C5;
Scope of a variable
A variable has always a scope in that sense that it is either global or local. Global will make the variable available document wide, whilst local, i..e in a block of code, will make the variable available in precisely the block of code that it is defined in.
A local variable can override one that was defined in a previous code block.
We can conveniently use a global variable, that has not been initialized in the beginning of a document and then initialize it instead in the local block.
Global variables have a constraint.
- Variables should be Lower case, but when concatenating it is best to use camelCase.
- A variable has to be written in one word, and has to start with a letter
- Words that start with capital letters are reserved for classes.
- It is not allowed to put punctuation marks in variable names, with the exception of underscores.
- The term “width” is a recognised variable in processing, among some others such as height. When using them they will be coloured in the built-in syntax highlighting. We can declare our own on top of those, and our own variable will replace the system function, which is a bad idea in general and not recommended.