Learn to Write Code
Real Code

See how real systems are actually built.

Ever wondered how a search engine ranks results, or how a payment gets approved, challenged, or blocked in real time? Each video below builds one real-world system end to end -- same pseudocode-first approach as the curriculum, just applied to something you already use.

REAL-WORLD BUILD

Ever wondered how an online shopping cart totals your order?

Use lists and loops to build a working e-commerce shopping cart that calculates totals and applies discounts.

Every major e-commerce platform — Amazon, Shopify, eBay — uses these exact patterns: collect items, loop through them, sum their prices, and apply rules.

You'll learn:LIST WITH for storing multiple valuesFOR EACH loops to process every itemRunning total pattern for summing pricesConditional discounts based on thresholds
REAL-WORLD BUILD

Ever wondered how a search engine decides which result to show first?

Score pages by importance and sort by relevance using maps, loops, and weighted scoring actions.

Search engines, product recommendation feeds, and social media algorithms all use ranking pipelines: score each candidate, then sort by score.

You'll learn:MAP WITH for named data signalsWeighted scoring with multipliersFOR EACH loops for candidate processingMax-tracking patterns for finding winners
REAL-WORLD BUILD

Ever wondered how a maps app picks your route out of dozens of options?

Compare multiple path options, score each by feasibility, and select the best route using composed actions.

The same scoring-and-selection pattern that powers Google Maps, Apple Maps, and Waze also applies to any multi-option decision, like picking the fastest CI/CD build or the best flight price.

You'll learn:Scoring route options with multiple signalsComposed actions for reusable logicBest-option selection patternsUser preference adjustments to scores
REAL-WORLD BUILD

Ever wondered how a feed decides what to show you next?

Score candidate items against user interests and filter for quality before showing the strongest matches.

YouTube recommendations, Netflix picks, Spotify playlists, and Amazon suggestions are all built on the same scoring, filtering, and ranking patterns.

You'll learn:User profile maps for interest weightsItem scoring based on user preferencesThreshold filtering for quality controlTop-N selection for final rankings
REAL-WORLD BUILD

Ever wondered how a payment gets approved, challenged, or blocked in real time?

Combine rule engines, risk scoring, and multi-outcome decisions to approve, verify, or block payments.

Every credit card transaction is scored this way — Stripe, Square, PayPal, and banks all run fraud engines before accepting or challenging a payment.

You'll learn:Rule-based risk scoring with signalsAdditive scoring for combined signalsMulti-outcome branching logicCapstone composition of variables, loops, lists, maps, and actions
Practice

Practice the concepts.

These prompts come directly from the concept lessons. Try answering in plain English or pseudocode first; then implement your answer in whichever language you are learning.

Lesson 1

Variables

Imagine a game score. What variable name would you use, and what value should it have when the game starts?

Lesson 2

Operators

What remainder should 17 MODULUS 5 produce?

Lesson 3

Input & Output

Think of one question a program could ask you and one thing it could display afterward.

Lesson 4

Sequence

Write three plain-English steps for making a sandwich in the order they must happen.

Lesson 5

Conditions

Create a plain-English IF/OTHERWISE decision for whether you should wear a coat.

Lesson 6

Loops

If a counter starts at 1 and you add one after every repetition, what condition would make it stop after displaying 10?

Lesson 7

Functions

What two pieces of information would an ACTION named CalculateArea need for a rectangle?

Lesson 8

Objects

If Car were a blueprint, name two pieces of data that each Car object might store.

Lesson 9

Lists

Given a list of colors ["Red", "Green", "Blue"], which index would get you "Green"? What would the list contain after you ADD "Yellow" to it?

Lesson 10

Strings

If a city name is stored in a variable called city, write the JOIN expression that would produce "Welcome to " followed by the city name and a period.

Lesson 11

Errors

Rewrite the withdrawal example so it throws a problem when withdrawal is a negative number instead of when it exceeds the balance.

Lesson 12

Recursion

What is the base case in CalculateFactorial, and what would happen if you removed it?

Lesson 13

Inheritance

If a Cat blueprint also EXTENDS Animal with its own MakeSound action, what would CALL ACTION myCat.MakeSound show?

Want to actually run what you write instead of just reading it? Coders Rock is a free browser-based practice site with pseudocode, Python, and JavaScript challenges matched to these same lessons -- no account needed.