arrays lists of values

An array is a list of values.

Array Literals

Here is an example of an array.

p = [2, 3, 5, 7, 11]

This array contains five numbers, so p.length is 5. Places in an array are counted from zero, so the first value is treated as the "0th" value p[0] (the value is 2) and the last value is the "4th" value p[4] (the value is 11).

write p.length
write "0th:", p[0]
write "4th:", p[4]

Notice that what we might normally call the "5th" value is counted as the 4th in a computer array that starts with 0.

Repeating For Each Value in an Array

for and in can be used to repeat some code for each value in an array. For example:

for x in p
  write x, "is prime"

Here x is a looping variable and takes on each value in the array, one at a time, while the part of the program in the loop body is repeated.

We can use any name for a looping variable.

Read more about for on the for reference page.