Computer Science

73 guides

Programming and algorithms

• Algorithm visualizer: sorting and pathfinding step by stepWatch six sorting algorithms and four pathfinding searches run step by step, with comparison and swap counts, big O, and the real code beside them.
• Binary search tree: insert, search, delete and traversalHow a binary search tree works: the ordering rule, searching, inserting and deleting, in-order, pre-order and post-order traversal, and Big O, with code.
• Conditional statements in programming: if, else and logicHow conditional statements in programming work: if, elif and else, comparison operators, AND, OR and NOT, truth tables, with Python and JavaScript code.
• Data types in programming: integer, real, Boolean, stringThe main data types in programming: integer, real (float), Boolean, character and string, with examples, how to choose one, casting and static typing.
• Hash table: how hashing, collisions and dictionaries workHow a hash table works: hash functions, collisions, chaining and linear probing, load factor, O(1) lookups and dictionaries in Python and JavaScript.
• Sorting algorithms: bubble, merge, quick sort and Big OHow the main sorting algorithms work: bubble, insertion, merge and quick sort, traced step by step, with time complexity and a visualiser to watch them.
• Variable scope and functions: local and global explainedWhat variable scope means, how local and global variables differ, and how functions, parameters, return values and the call stack work, with code to run.

Data and logic

• Binary calculator: convert and add binary numbersConvert binary to decimal, hex and octal and back, and add binary numbers with the carries shown, with the working and examples to check.
• Boolean algebra calculator: simplify with laws and K-mapsFree Boolean algebra calculator: simplify any expression step by step, with each law named, a Karnaugh map, and the minimal sum of products.
• Hex to decimal converter: hexadecimal with workingConvert hexadecimal to decimal and back, and hex to binary, with place values, repeated division and nibble grouping, plus worked examples.
• Karnaugh map solver: K-map simplification with groupsFree Karnaugh map solver: draw the K-map for up to 4 variables, see the groups, and get the minimal sum of products or product of sums, with don't cares.
• Logic gate simulator: build circuits, see the truth tableBuild logic circuits from AND, OR, NOT, NAND, NOR and XOR gates, flip switches and watch the signals, with a live truth table and an expression per lamp.
• Truth table generator: any logic expression with stepsMake a truth table for any logic expression in AND OR NOT, logic symbols or · + ′ notation, with a column per step and canonical forms.
• Two's complement calculator: signed binary and IEEE 754Free two's complement calculator: convert signed numbers between decimal, binary and hex at 8, 16 or 32 bits, and see IEEE 754 floats field by field.

Computer systems

• CPU simulator: fetch, decode, execute in assemblyFree CPU simulator: write a short assembly program and step through the fetch-decode-execute cycle, with registers, memory and buses lit as they are used.
• How does a CPU work? Fetch, decode, execute explainedHow a CPU works, step by step: the fetch, decode, execute cycle, the registers it uses, and why clock speed, cores and cache make it faster.
• Random access memory (RAM): what it is and how it worksWhat random access memory (RAM) does, why it is volatile, RAM vs ROM and storage, cache, DRAM vs SRAM, and how to work out RAM bandwidth.
• Storage devices: HDD vs SSD, magnetic and solid stateHow storage devices work: magnetic hard drives, solid state drives, SATA and NVMe, cloud storage, and how to work out load times.
• What does a quantum computer look like? Qubits explainedWhat a quantum computer looks like and why it is so cold, what a qubit is, how quantum computers differ from normal ones, and how you can use one online.
• What is a logic gate? Types, truth tables and symbolsWhat a logic gate is, the 7 types with truth tables, how gates combine into circuits and adders, Boolean notation, and a free simulator to try them.
• What is quantum entanglement? A simple explanationWhat quantum entanglement is, how it works, whether it is real, how it is measured, why it can't send messages faster than light, and its uses.
• What is superposition? In waves and in quantum physicsWhat superposition means: the principle of superposition for waves, where displacements add, and quantum superposition, where a qubit holds 0 and 1.

Networks

• How does the internet work? Packets, routers and protocolsHow the internet works, step by step: packets, routers, IP addresses, DNS, TCP and HTTP, the TCP/IP model and the cables that carry it all.
• TLS encryption: how TLS and SSL keep HTTPS secureHow TLS encryption works: SSL vs TLS, the TLS handshake, certificates, symmetric and asymmetric keys, and a Diffie-Hellman key exchange worked through.
• What is a DNS server? How DNS turns names into IPsWhat DNS stands for, what a DNS server does, how a domain name is resolved step by step, what the DNS cache is and how to clear it, and record types.
• What is a MAC address? Format, examples and lookupWhat a MAC address is, how to read one, what the first half tells you about the maker, how it differs from an IP address, and how to find yours.
• What is a subnet mask? Meaning, examples and cheat sheetWhat a subnet mask is, how it splits an IP address, how to work out the network and host range by hand, plus a /8 to /32 cheat sheet.
• What is an IP address? IPv4, IPv6 and how to find yoursWhat an IP address is and how it works: IPv4 and IPv6, public vs private, static vs dynamic, what your IP reveals and how to find yours.
• What is TCP? How it works, the handshake and TCP vs UDPWhat TCP is, how the three-way handshake, sequence numbers and resends make data arrive in order, the TCP/IP model, and TCP vs UDP with examples.

Databases

• CASE WHEN in SQL: syntax and examplesHow CASE WHEN works in SQL: both forms of the syntax, ELSE and NULL, and examples in SELECT, ORDER BY, GROUP BY counts and UPDATE, with results shown.
• How does a relational database handle indexing? B-treesHow relational databases use indexes to find rows fast: B-tree indexes, clustered and secondary indexes, the query planner, and the cost of indexes.
• SQL practice online: 9 exercises with answersFree SQL practice online: two small tables and nine exercises, from SELECT and WHERE to GROUP BY, HAVING and JOINs, each with the query and the result.
• What is a database? Types, software and examplesWhat a database is, how tables, records and fields work, what database software (a DBMS) does, the main types of database and a first SQL query.
• What is a relational database? Tables, keys and joinsWhat a relational database is: tables linked by primary and foreign keys, one-to-many and many-to-many relationships, SQL joins and why it avoids repeats.
• What is a vector database? How it works, with examplesA vector database stores embeddings and finds the most similar items fast. Learn how vector search works, ANN indexes like HNSW, RAG and real uses.
• What is SQL? What it is used for, with simple examplesSQL is the language for asking databases questions. Learn what SQL is, what it is used for, the main commands and how queries work, with examples.

Web and APIs

• HTML stands for HyperText Markup Language: what it meansHTML stands for HyperText Markup Language. What each word means, how tags and elements work, who invented HTML, and related acronyms like HTTP and CSS.
• Is HTML a programming language? Markup vs programmingIs HTML a programming language? Why it is a markup language instead, how it differs from JavaScript, and whether writing HTML counts as coding.
• Online code editor for HTML, CSS and JavaScriptWrite HTML, CSS and JavaScript in your browser and see the page and console live, with coding problems that check your answer and a link to share.
• What does API stand for? APIs explained with examplesWhat API stands for, how an API works, what an API call is, with a real request and response, plus API types, API access and API testing.
• What is an API key? Meaning, examples and keeping it safeWhat an API key is, how it works in a real request, how it differs from a token, how to get one for Gemini or OpenAI, and how to keep it safe.
• What is JavaScript used for? Uses and examplesWhat JavaScript is used for: interactive websites, web apps, servers, mobile and desktop apps and games, with a working example and how it fits with HTML.
• What is React? The JavaScript library explained simplyReact is a free JavaScript library for building user interfaces from components. Learn what React is used for, how it works, with code examples.

Cyber security

• How do you prevent SQL injection attacks? 7 key defencesHow to prevent SQL injection: parameterised queries, allow-lists, least privilege and more, with safe code in Python, Node.js, Java and PHP.
• What is a social engineering attack? Types and examplesA social engineering attack tricks people instead of computers. The main types with examples, the pressures they rely on, and how to defend yourself.
• What is blockchain? How it ensures immutabilityWhat a blockchain is and how it makes records so hard to change: hashes that chain blocks, proof of work, thousands of copies, and where its limits are.
• What is data encryption? How it works, with examplesWhat data encryption is, how plaintext becomes ciphertext with a key, Caesar and one-time pad examples, symmetric vs public key encryption, and its uses.
• What is hacking? Types of hackers and ethical hackingWhat hacking is, the types of hackers, how attacks work, what ethical hacking is, how to learn it legally, and how to protect yourself.
• What is spear phishing? Examples, signs and how to stop itSpear phishing is a targeted scam built around you or your job. See real examples, the warning signs, how it differs from phishing and how to stop it.

Electronics

• How to make an Arduino-based robot: parts, wiring and codeHow to make an Arduino-based robot that avoids obstacles: the parts, why it needs a motor driver, wiring, PWM speed control and a full example sketch.
• How to set up a Raspberry Pi as a web server: step by stepSet up a Raspberry Pi as a web server: install the OS, connect over SSH, install nginx, publish your page, add HTTPS and keep it secure.
• How to use I2C on Arduino: wiring, Wire library, codeHow to use I2C on Arduino: which pins to wire, pull-up resistors, device addresses, the Wire library, an I2C scanner and reading a sensor.
• What is a breadboard used for? How breadboards workWhat a breadboard is used for, how its rows, power rails and centre gap connect inside, how to build a first LED circuit on one, and common mistakes.
• What is a microcontroller? How MCUs work, with examplesA microcontroller is a tiny computer on one chip that runs one program to control a device. See what is inside, how it works, and the boards to start with.
• What is Arduino? Uno, pins, IDE and Arduino vs ESP32What Arduino is, how the Uno and its pins work, the Arduino IDE, the limits of Arduino, and the difference between Arduino and ESP32.

Courses

• API course: HTTP, JSON, REST and fetch for beginnersAn interactive API course in 32 short sections: HTTP methods, endpoints, requests and responses, JSON, status codes, REST, API keys, Express and fetch.
• Arduino course: microcontrollers from blink to Wi-FiAn interactive Arduino course in 26 short sections: boards, sketches, digital and analog pins, buttons, PWM, 5 V and 3.3 V logic, ESP32 Wi-Fi, I2C and SPI.
• Basic electronics course: circuits and logic gatesAn interactive basic electronics course in 28 short sections: Ohm's law, series and parallel, dividers, capacitors, LEDs, logic gates and Boolean algebra.
• Computer graphics course: from triangles to pixelsAn interactive computer graphics course in 25 sections: GPUs, meshes, the rendering pipeline, matrices, rasterisation, shaders, depth and lighting.
• Computer hardware course: every PC component explainedAn interactive computer hardware course in 36 sections: CPU, cache, RAM, storage, GPU, motherboard, power supply, cooling and overclocking.
• Database course: SQL, keys, joins and design for beginnersAn interactive database course in 28 short sections: tables and primary keys, SQL queries, CRUD, relationships, joins, SQL vs NoSQL, migrations and ORMs.
• Ethical hacking course: web security for beginnersAn ethical hacking course on web security: the law and ethics, how common website weaknesses work, and how developers defend against them, in 26 sections.
• Hardware security course: threats to devices and defencesA hardware security course in 25 short sections: side channels, faults, debug ports, secure boot, supply chains and tamper resistance.
• HTML, CSS and JavaScript course for complete beginnersA short, interactive HTML, CSS and JavaScript course for beginners: tags, nesting, CSS rules, the box model, flexbox, functions and loops, in 15 sections.
• IP addressing course: subnets, ports, NAT, DHCP and DNSAn interactive IP addressing course in 25 short sections: octets and bits, subnet masks and CIDR, host counts, ports, TCP and UDP, NAT, DHCP, DNS and IPv6.
• Learn binary and hexadecimal: an interactive courseLearn binary and hex in 24 short sections: place value, binary, decimal and hex conversions, bits and bytes, binary addition, overflow and colour codes.
• Networking course: switches, routers, Wi-Fi and cablesAn interactive networking course in 26 short sections: NICs and MAC addresses, switches, routers, NAT, Wi-Fi, modems, firewalls, topologies and OSI.
• Programming languages course: compare, choose and understandAn interactive programming languages course in 28 short sections: compiled vs interpreted, static vs dynamic typing, OOP vs functional, and memory.
• Raspberry Pi course: set up, GPIO, Python and projectsAn interactive Raspberry Pi course in 30 short sections: set up a Pi 5, use Linux, wire LEDs and buttons to the GPIO pins and code them in Python.
• Search algorithms course: binary search, Big O, BFS and DFSAn interactive search algorithms course in 24 short sections: linear and binary search, Big O notation, hash tables, trees and graphs, and BFS vs DFS.
• Social engineering course: spot and stop scamsA social engineering course in 24 short sections: why scams work, phishing, lookalike links, scam calls, deepfakes, and how to defend and report.
• Web frameworks course: React, Next.js, Express explainedAn interactive web frameworks course in 25 sections: SPAs, React components, props and state, Next.js rendering and routing, Express and the full stack.
• Web hosting course: deploy a website from Git to HTTPSAn interactive web hosting course: DNS, static and dynamic hosting, Git deploys, CI/CD, secrets, Docker, HTTPS and monitoring, in 30 short sections.