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Array access

Learn 0-based indexing and O(1) access.

Looping through an array

To visit every element of an array, use a for x in arr: loop. This processes each element in order.

If you also need the index, write for i in range(len(arr)):. This lets you use both the index and the element.

Printing an array

To print each element on its own line, call print(x) inside the loop. This takes O(n) time.

To see the whole array on one line, print(arr) is enough; it shows the list representation of the array.

Practice Print array

Write print_all(arr). Print each element with for. Call print_all([5, 10, 15]) to print 5, 10, 15.

Starter code

solution.py
def print_all(arr):
    # Print each element

Sample solution

solution.py
def print_all(arr):
    # Print each element
    for x in arr:
        print(x)
print_all([5, 10, 15])

Expected output

5
10
15

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Loop structure

Question 
To iterate array elements: ____ x in arr:
Answer 
To iterate array elements: for x in arr:

Explanation: for is right.

2 Array access: match the terms

Term Meaning
for Loop
len(arr) Length
range Range
print Print

3 What does len(arr) return?

  • The first element
  • The last element
  • The number of elements Correct answer
  • The index

Explanation: len(arr) returns the number of elements.

All lessons in Beginner

1 What is an algorithm?

  1. Algorithm definition
  2. Algorithm properties
  3. Pseudocode
  4. Summary - Algorithm concept

2 Big-O notation

  1. Time complexity
  2. Big-O definition
  3. Comparing complexities
  4. Summary - Big-O

3 Array

  1. What is an array?
  2. Array access
  3. Looping over an array
  4. Summary - Arrays

4 Linear search

  1. Linear search idea
  2. Implementing search
  3. Best and worst case
  4. Summary - Linear search

5 Search project

  1. Project: Overview
  2. Grades array setup
  3. Search function
  4. Print the result

6 Bubble sort

  1. Bubble sort idea
  2. One pass
  3. Full sort
  4. Summary - Bubble sort

7 Selection sort

  1. Selection sort idea
  2. Finding the minimum
  3. Swapping
  4. Summary - Selection sort

8 Insertion sort

  1. Insertion sort idea
  2. Shifting
  3. Placement
  4. Summary - Insertion sort

9 Sorting project

  1. Project: Overview
  2. Price array
  3. Apply sorting
  4. Print the result

10 Recursion basics

  1. What is recursion?
  2. Base case
  3. Recursive step
  4. Summary - Recursion

11 Fibonacci

  1. Fibonacci sequence
  2. Recursive Fibonacci
  3. Call tree
  4. Summary - Fibonacci

12 Factorial

  1. Factorial definition
  2. Recursive factorial
  3. Choosing the base case
  4. Summary - Factorial

13 Recursion project

  1. Project: Overview
  2. Recursive power
  3. Combination
  4. Print the results

14 Binary search

  1. Binary search idea
  2. Left right pointers
  3. Base case
  4. Summary - Binary search

15 Linked list

  1. What is a linked list?
  2. Node definition
  3. Traversing the list
  4. Summary - Linked list

16 Stack

  1. What is a stack?
  2. Push and pop
  3. Peek and is_empty
  4. Summary - Stack

17 Queue

  1. What is a queue?
  2. Enqueue and dequeue
  3. Front and back
  4. Summary - Queue

18 Hash table

  1. What is a hash table?
  2. Hash function
  3. Collision
  4. Summary - Hash table

19 Set

  1. What is a set?
  2. Add and lookup
  3. Intersection and union
  4. Summary - Set

20 Beginner final

  1. Challenge 1
  2. Challenge 2
  3. Challenge 3
  4. Challenge 4