6.3: Loops with Arrays
Learning Objectives
By the end of this lesson, you should be able to:
Use the built-in
.length
array property.Use either a while or for loop to access or manipulate elements of an arbitrary-length array.
Introduction
Often we want to perform actions on all elements of arrays of arbitrary length. We can use loops to run code on each array element sequentially.
The trick to using loops with arrays is to link the counter
loop concept with the index
array concept. Typically, the counter represents the current index of the array, and the length of the array is the maximum counter value plus 1. The "plus 1" is because array indexes are 0-indexed, thus the maximum valid array index is the array length minus 1.
Looping Over Arrays
To get the length of an array, we can use the .length
method. This method exists on every array.
In the following example we use letters.length
to determine the number of loop iterations. We use index
to access each element in the array sequentially, 1 element per loop iteration.
Address Book Example
Let's create a practical example of loops with arrays using an address book. Our address book stores unique names in an array, i.e. will not add a name if it is already in the book.
Exercises
Follow Along
Implement the above code.
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