Every computer program requires the computer to store some form of data. In Grace, the simplest ways to store a value are either in a variable, or in a definition.
A definition creates a name for a value. This value can be anything, from the number of sides of a polygon to the name of the city where you were born. To make a definition, simply do the following:
def triangleSides = 3
def city = "Portland"
A variable is like a definition, but it can be changed (hence the name “variable”).
Since the value of a variable can be changed, it doesn’t make sense to use =
when declaring one (even though many other programming languages
do this; future programmers beware). Instead, variables are assigned a
value using the assignment symbol := (pronounced “gets”). For instance:
var weight := 140
var favoriteSong := "You are my sunshine"
If a variable already exists, it can be reassigned a value. Note that since it
has already been created, you need to specify only the name, and don’t need to repeat
the var. So an assignment looks like this:
favoriteSong := "Somewhere over the rainbow"
Variables can store all kinds of data, including Numbers, Strings
(Grace’s representation of text), and Booleans (true and false).
Look at the examples below. Now edit them and try changing the values.