Arrays and lists in Intro to Computing - Draw & Build Visually

Draw This - beginner

Draw a diagram showing an array of 5 numbers: [10, 20, 30, 40, 50]. Label each element with its index (0 to 4).

5 minutes

Hint 1

Hint 2

Hint 3

Grading Criteria

Diagram shows 5 boxes in a row

Each box contains one number from the list

Indexes labeled from 0 to 4 below the boxes

Boxes are connected in a single horizontal line

Solution

  +-----+-----+-----+-----+-----+
  | 10  | 20  | 30  | 40  | 50  |
  +-----+-----+-----+-----+-----+
    0     1     2     3     4  

This diagram shows an array as a row of boxes. Each box holds one number from the list.

The numbers are 10, 20, 30, 40, and 50.

Below each box is its index, starting from 0 on the left to 4 on the right.

This helps us find values quickly by their position.

Variations - 2 Challenges

[beginner] Draw a diagram showing a list of 4 fruits: ["apple", "banana", "cherry", "date"]. Label each element with its position starting at 1.

[intermediate] Draw a diagram showing an array of 6 numbers: [5, 15, 25, 35, 45, 55]. Label each element with its index (0 to 5) and show how to access the element at index 3.

Practice

1. What is the position of the first item in an array or list?

easy

A. 0

B. 1

C. Depends on the list size

D. Last position

Solution

1. Step 1: Understand list indexing

   Arrays and lists start counting positions from zero, not one.

2. Step 2: Identify the first position

   The first item is always at position 0 in the list.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   First position = 0 [OK]

Hint: Remember counting starts at zero in lists [OK]

Common Mistakes:

• Thinking first position is 1
• Confusing position with size
• Assuming last position is first

2. Which of the following is the correct way to add an item 'apple' to a list named fruits in Python?

easy

A. fruits.insert('apple')

B. fruits.add('apple')

C. fruits.append('apple')

D. fruits.push('apple')

Solution

1. Step 1: Recall Python list methods

   To add an item at the end of a list, Python uses the append() method.

2. Step 2: Match method to syntax

   fruits.append('apple') correctly adds 'apple' to the list.

3. Final Answer:

   fruits.append('apple') -> Option C

4. Quick Check:

   Use append() to add items [OK]

Hint: Use append() to add items at list end [OK]

Common Mistakes:

• Using add() which is for sets
• Using push() which is JavaScript
• Using insert() without position

3. What will be the output of this Python code?

numbers = [10, 20, 30, 40]
print(numbers[2])

medium

A. 30

B. 20

C. 40

D. 10

Solution

1. Step 1: Identify the index used

   The code accesses numbers[2], which means the item at position 2.

2. Step 2: Find the item at index 2

   Positions start at 0: numbers[0]=10, numbers[1]=20, numbers[2]=30.

3. Final Answer:

   30 -> Option A

4. Quick Check:

   Index 2 value = 30 [OK]

Hint: Count from zero to find index value [OK]

Common Mistakes:

• Counting from 1 instead of 0
• Confusing index with value
• Choosing last item by mistake

4. Find the error in this Python code that tries to print the last item of a list named colors:

colors = ['red', 'green', 'blue']
print(colors[3])

medium

A. SyntaxError due to wrong brackets

B. IndexError because index 3 is out of range

C. prints 'blue' correctly

D. TypeError because colors is not a list

Solution

1. Step 1: Check list length and index

   The list has 3 items at indexes 0, 1, and 2. Index 3 is beyond the last item.

2. Step 2: Understand error type

   Accessing index 3 causes an IndexError because it is out of range.

3. Final Answer:

   IndexError because index 3 is out of range -> Option B

4. Quick Check:

   Index out of range = IndexError [OK]

Hint: Last index is length minus one [OK]

Common Mistakes:

• Using wrong index number
• Thinking index 3 is valid
• Confusing error types

5. You have a list of daily temperatures: temps = [22, 19, 24, 21, 20]. How can you create a new list with only temperatures above 20 using Python list comprehension?

hard

A. [temp > 20 for temp in temps]

B. [temp for temp in temps where temp > 20]

C. [temp if temp > 20 for temp in temps]

D. [temp for temp in temps if temp > 20]

Solution

1. Step 1: Understand list comprehension syntax

   The correct syntax is: [expression for item in list if condition].

2. Step 2: Apply condition to filter temps

   Use temp for temp in temps if temp > 20 to select temps above 20.

3. Final Answer:

   [temp for temp in temps if temp > 20] -> Option D

4. Quick Check:

   Filter with if inside comprehension [OK]

Hint: Use if after for in list comprehension [OK]

Common Mistakes:

• Placing if before for
• Using > 20 inside list without if
• Using where instead of if