-
Sometimes we want to ask questions about data. For example, is
x
greater thany
? Is one string equal to another? These questions can’t be answered with Numbers. Instead, they are answered with a new data type called a Boolean. -
video games use Booleans for many things: asking when a player’s health is equal to zero, whether two characters are close enough to bump into one another, or if a character’s coordinates put it off the edge of the screen.
-
A Boolean value is either
true
orfalse
. Unlike Numbers, Strings, and Images, Booleans have only two possible values. -
You already know some functions that produce Booleans, such as
<
and>
! Our programming language has them, too:(< 3 4)
,(> 10 2)
, and(= -10 19)
. -
We also have ways of writing Compound Inequalities, so we can ask more complicated questions using the
and
andor
functions.-
(and (> 3 4) (< 10 2))
translates to "three is greater than four and ten is less than two". This will evaluate tofalse
, since theand
function requires that both sub-expressions betrue
. -
(or (> 3 4) (< 10 2))
, which translates to "three is greater than four or ten is less than two". This will evaluate totrue
, since theor
function only requires that one sub-expression betrue
.
-
-
The Circles of Evaluation work the same way with Booleans that they do with Numbers, Strings and Images:
and > 3 4 < 10 2 (and (> 3 4) (< 10 2))or > 3 4 < 10 2 (or (> 3 4) (< 10 2))
These materials were developed partly through support of the National Science Foundation,
(awards 1042210, 1535276, 1648684, and 1738598).
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