LISTS IN SNAP
What is a List?
• A list is an ordered set of
elements, where each
value is identified by an
index
• Elements can be
anything (numbers,
letters, words, pictures,
lists, etc.)
Lists in Snap
• On the Variables tab, make a variable, and give it a name
• Set it to a List block (below)
• Show and hide the list on the screen
• You can add to the list when it’s on screen:
• Create a list in your script with the list reporter block:
• Can be used without creating a list variable first
• Use the arrows to add/remove items, and type them in
• Can be set to a variable (that wasn’t originally a list):
Working with Lists and Elements
• Add an element to the end
• Remove an element
• Insert an element at index
• Replace an element at index
• Retrieve/report an element
• Get the number of elements
• See if a list contains an element
• Convert list to text
• Make a copy of a list
Walking lists
• Use code to visit each element
• Create variables for index and
length
• Use a Repeat loop counting up
until index > length
• Inside the loop, do your work
• Could also use our custom For
loop we made awhile back…
Or, using a For each loop, built just for lists
Extra List blocks
• On the File menu, choose Import tools
• You now have new blocks on the Variables and Operators
tabs that work with lists
• Explore using these, as you'll need them in the Hangman
project
• For loop is added here as well (so you don't have to use
the custom block we built)
Assignment
• No handout today, just a practice coding assignment
• Create a variable, set it to a list
• Create a new block AddItems to add up the items in the list
• AddItems should walk each element, adding to a Sum variable,
and report it back
• What kind of custom block is AddItems (Command, Reporter, or
Predicate)?
• What are its inputs?
• What does it report back? Remember to set this before you’re done…
• Extra challenges
• Check to make sure the inputs are numbers or handle errors