Boolean

A value that's either true or false.

Boolean values help to make decisions in code. They appear any time a logical condition is checked. For example, the condition "Is a mouse button being pressed?" must be either true or false:

-- If the user presses the mouse, draw a circle at
-- the mouse's location.
if mouseIsPressed == true then
  circle(mouseX, mouseY, 20)
end

The if statement checks whether mouseIsPressed is true and draws a circle if it is. Boolean expressions such as mouseIsPressed == true evaluate to one of the two possible Boolean values: true or false.

The == operator (EQUAL) checks whether two values are equal. If they are, the expression evaluates to true. Otherwise, it evaluates to false.

The mouseIsPressed system variable is always true or false, so the code snippet above could also be written as follows:

if mouseIsPressed then
  circle(mouseX, mouseY, 20)
end

The ~= operator (NOT EQUAL) checks whether two values are not equal, as in the following example:

if 2 + 2 ~= 4 then
  text('War is peace.', 50, 50)
end

Starting from the left, the arithmetic expression 2 + 2 produces the value 4. The Boolean expression 4 ~= 4 evaluates to false because 4 is equal to itself. As a result, the if statement's body is skipped.

The Boolean operator and checks whether two expressions are both true:

if keyIsPressed == true and key == 'p' then
  text('You pressed the "p" key!', 50, 50)
end

If the user is pressing a key AND that key is 'p', then a message will display.

The Boolean operator or checks whether at least one of two expressions is true:

if keyIsPressed == true or mouseIsPressed == true then
  text('You did something!', 50, 50)
end

If the user presses a key, or presses a mouse button, or both, then a message will display.

The following truth table summarizes a few common scenarios with and and or:

true and true  -- true
true and false -- false
false and false -- false
true or true  -- true
true or false -- true
false or false -- false

The relational operators >, <, >=, and <= also produce Boolean values:

2 > 1 -- true
2 < 1 -- false
2 >= 2 -- true
2 <= 2 -- true

See if for more information about if statements and number for more information about numbers.