Learn to Program with Small Basic

Associative Arrays
In the previous chapter, you learned how to use an integer index to access
an array’s elements. But in Small Basic, an array’s index can also be a string.
Arrays indexed by strings are called associative arrays, maps, or dictionaries.
In this book, we’ll call them associative arrays. Just like an indexed array,
an associative array can store values of any type. You can use an associative
array to create an association between a set of keys (string indices) and a set
of values, which is called creating a map of key-value pairs.
The following code shows a simple example of an associative array in
action. It’s a list of states keyed by their two-letter abbreviations:
state["CA"] = "California"
state["MI"] = "Michigan"
state["OH"] = "Ohio"
' ... and so on
To display the name of a state, you simply use its corresponding key
and the proper syntax. For example, to display Michigan, you can write this
statement:
TextWindow.WriteLine(state["MI"])
By writing the name of the array followed by the key enclosed in square
brackets, you can access the corresponding item. An associative array works
like a lookup table that maps keys to values; if you know the key, you can find
its value very quickly.
To learn how to use associative arrays, let’s write a program that keeps
track of the ages of your friends by name. Enter the program in Listing 16-1.
1 ' AssociativeArray.sb
2 age["Bert"] = 17
3 age["Ernie"] = 16
4 age["Zoe"] = 16
5 age["Elmo"] = 17
6 TextWindow.Write("Enter the name of your friend: ")
7 name = TextWindow.Read()
8 TextWindow.Write(name + " is [")
9 TextWindow.WriteLine(age[name] + "] years old.")
Listing 16-1: Using associative arrays
Lines 2–5 create an associative array named age with four elements in
it. You can add more if you’d like, or you can change the array to store the
ages of your own friends. Line 6 asks you to enter a friend’s name, and line
7 reads it into the name variable. In line 9, age[name] looks up the age of that
friend.
228 Chapter 16