1.1.7 traversing turtles

list

An ordered collection of items or values. For example, [value1, value2, value3, …] describes a list where value1 is the first element, value 2 is the second element, value 3 is the third element, and so on. 

array

An ordered collection of elements of the same type.  

literal

A literal is a fixed value in source code, such as 5 or "hello".  

list element

An individual value in a list that is assigned a unique index.  

loop variable

In each iteration step, a variable set to a value in a sequence or other data collection.  

lists concept

• We use these to group data types with a construct known as a list. 

• Some other programming languages refer to a list as an array. 

  • ANYTHING CAN BE GROUPED TOGETHER IN A LIST

    • Numbers, words, fruits, animals, colors. 

How college board uses the following to represent assigning values to a list 

aList ← [value1, value2, value3...]

This creates a new list that contains the values value1, value2, value3, and … at indices 1, 2, 3, and … respectively and assigns it to aList.

aList ← []

Creates a new empty list and assigns it to aList.

You can also copy a list to another list. 

aList ← bList

This assigns a copy of the list bList to the list aList. For example, if bList contains [20, 40, 60], then aList will also contain [20, 40, 60] after the assignment.

how do you add an e;ement to the end of a list?

• You can do this using the append method. 

• The College Board uses APPEND(aList, value)  to represent adding items to a list.

how do you get the last item that was placed into the list and remove it, much like you would grab the top item out of a basket or bag?

• You use the pop method

• It removes the last element of the list and assigns it to a variable. 

how do you repeat a task for each item in the list?

• By using a for loop. 

  • A for loop retrieves each element from the list and assigns it to the loop variable. 

    • Using the loop variable, you can have the program execute the same set of statements for each element. In effect, the loop variable can be assigned to each element of a list on each interaction of the list. 

    • The College Board uses the following notation to represent a for loop:

    • FOR EACH item IN aList

    • {

    •     <block of statements>

    • }

• Assume you have a list of numbers such as a_list= [1,2,3,4,5]

• Which of the following statements will add a new number to the list? 

  • a_list=a_list +6

  • a_list=(6)

  • a_list.append(6)

  • a_list.add(6)

C

• Assume that you have a list of numbers such as a_list=[1,2,3,4,5]

• Select the for statement that iterates through the list. 

  • For num in a_list: 

  • For (num,a_list): 

  • For each (num in a_list): 

  • For each (num,a_list):

A

• Assume that you have a list of numbers such as a_list= [1,2,3,4,5]

• What would  the value of num be after the following code? 

• num=a_list.pop()

• num=a_list.pop()

  • 1

  • 2

  • 4

  • 5

C