Stacks (last-in, first-out) in Intro to Computing - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an item to the top of the stack.

Intro to Computing

stack = []
stack.[1]('apple')

Drag options to blanks, or click blank then click option'

Aremove

Bpop

Cappend

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pop' which removes an item instead of adding.

Using 'remove' which deletes a specific item.

Using 'insert' which adds at a specific position, not necessarily the top.

To add an item to the top of a stack, we use the append method, which adds the item to the end of the list, representing the top of the stack.

2fill in blank

medium

Complete the code to remove the top item from the stack.

Intro to Computing

stack = ['apple', 'banana', 'cherry']
top_item = stack.[1]()

Drag options to blanks, or click blank then click option'

Apop

Bremove

Cappend

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' which adds an item instead of removing.

Using 'remove' which deletes a specific item by value.

Using 'insert' which adds an item at a position.

The pop() method removes and returns the last item from the list, which represents the top of the stack.

3fill in blank

hard

Fix the error in the code to check if the stack is empty.

Intro to Computing

stack = []
if len(stack) [1] 0:
    print('Stack is empty')

Drag options to blanks, or click blank then click option'

A!=

B==

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' which checks if stack is not empty.

Using '>' which checks if stack has items.

Using '<=' which includes zero and negative numbers (not relevant here).

To check if the stack is empty, we compare the length of the stack to zero using ==. If length equals zero, the stack is empty.

4fill in blank

hard

Fill both blanks to create a stack with numbers 1 to 5 and remove the top item.

Intro to Computing

stack = [[1] for num in range(1, 6)]
top = stack.[2]()

Drag options to blanks, or click blank then click option'

Anum

Bpop

Cappend

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' instead of 'pop' to remove the top item.

Using 'number' which is not defined.

Using 'num' incorrectly outside the comprehension.

The list comprehension uses num to add numbers 1 to 5 to the stack. Then, pop() removes the top item.

5fill in blank

hard

Fill all three blanks to create a stack from letters, add 'z', and then remove the top item.

Intro to Computing

stack = [[1] for [2] in ['a', 'b', 'c']]
stack.[3]('z')
top = stack.pop()

Drag options to blanks, or click blank then click option'

Aletter

Bx

Cappend

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the comprehension.

Using 'pop' instead of 'append' to add an item.

Using undefined variable names.

The list comprehension uses letter to loop through the list. Then append adds 'z' to the top of the stack.