Institute for Personal Robots in Education (IPRE)‏ CSC 170 Computing: Science and Creativity

We often need to store a collection of items Snap ! has the list block Found under Variables The following list has 3 elements It is considered an anonymous list as it has no nameno name LISTS 2

By default, a list has 1 item that is an empty word To create an empty list, click the left arrow to remove it NEW LISTS CAN HAVE ONE NOTHING ITEM 3

A NAMED LIST WITH 3 ELEMENTS 4 Code demo: Give a name to an “empty” list, add 3 names Show all, first, last, and any element in the list known as names names is a list with 0 elements

TIME MAGAZINE ARTICLE Many years ago, an historian asked me to come up with a list of random numbers, from 1 to 100 I used Turbo Pascal to do this, it took about 5 minutes because Turbo Pascal has a pseudo random number generator, like Snap ! does The list was then used to select from a list of the top 100 historians who would then supplied their top 5 list of the worst presidents in U.S. history Ronald Reagan made the list of the 5 worst presidents in a Time Magazine article My colleague received death threats and left Penn State Code demo: Create a custom block to return a list of random integers

ONE SOLUTION 6

You list of phone contacts List of s Your registered courses Your transcript A top ten list The list of movies in your NetFlix queue List of all addresses for the newspaper delivery person This list Snap list of lists Each element in a list is another list LISTS ARE USED EVERYWHERE 7

A SNAP! LIST OF LISTS 8

A lot of computer time is spent Searching for an item in a list Sorting a list SEARCHING AND SORTING LISTS 9

A data type is first class in a programming language if data of that type can be all of the following: the value of a variable an input to a block the value returned by a block a member of a data aggregate: we can have a list of lists anonymous (not named) Snap lists are first class types! LISTS ARE FIRST CLASS TYPES 10

Average of a list of numbers input to a block Set sum to 0 For every element in the list Add the item to sum report sum / length of the list ALGORITHM: AVERAGE OF A LIST OF NUMBERS 11

Minimum word of a list input to a block Set min to the first item in the list For every element in the list If that item is less than the min Change min report min Write a Snap block that does this ALGORITHM: FIND THE ALPHABETICALLY FIRST WORD 12