C_educator

Learn C the way it is actually written — one compiling file at a time.

16 progressive lessons · 40+ graded exercises with solutions · 3 build-it-yourself projects

No slides. No pseudocode. Every single file in this repository compiles and runs.

---

Why this repo exists

Most C tutorials stop at printf. The interesting part of C — the part that decides whether your program is correct or merely lucky — starts at pointers and does not end until you understand who owns which byte and when it gets freed.

C_educator walks that whole distance. Each lesson is a folder you can cd into, build with one command, and break on purpose. The exercises have real solutions, not hints. The projects are small enough to finish in an evening and large enough to teach you something.

   hello.c ──► ┌──────────────┐
               │ preprocessor │ ──► expanded source   gcc -E
               └──────────────┘
               ┌──────────────┐
               │   compiler   │ ──► assembly          gcc -S
               └──────────────┘
               ┌──────────────┐
               │  assembler   │ ──► object file       gcc -c
               └──────────────┘
               ┌──────────────┐
               │    linker    │ ──► executable        gcc
               └──────────────┘

Lesson 01 makes you run every one of those four stages by hand. After that you will never again wonder what "undefined reference" means.

---

Quick start

git clone https://github.com/limonuser/C_educator.git
cd C_educator

make            # build every lesson, project and solution
make lesson-09  # build just the pointers lesson
make run-09     # build it and run it
make clean      # remove all binaries

No compiler yet? See docs/SETUP.md — Linux, macOS and Windows covered in three commands each.

---

The curriculum

Work top to bottom. Each lesson assumes the one above it and nothing else.

Part I — The Language Floor

#	Lesson	You will learn	Key file
01	Hello, World	The four compilation stages, main's return value, what #include really does	hello.c
02	Variables & Types	Integer widths, overflow, float vs double, why int is not 32 bits by law	types.c
03	Operators	Precedence, integer division traps, bit manipulation, short-circuit evaluation	operators.c
04	Control Flow	if/else chains, switch fallthrough as a feature, the dangling-else trap	control.c
05	Loops	for/while/do-while, off-by-one errors, break vs continue, loop invariants	loops.c
06	Functions	Prototypes, pass-by-value, scope, recursion and its stack cost	functions.c

Part II — Memory, For Real

#	Lesson	You will learn	Key file
07	Arrays	Contiguous storage, bounds are your job, multidimensional layout	arrays.c
08	Strings	char * vs char[], the NUL terminator, why strcpy is a loaded gun	strings.c
09	Pointers	Address-of, dereference, NULL, pointer arithmetic, the type system's role	pointers.c
10	Pointers & Arrays	Array decay, arr[i] == *(arr+i), passing arrays to functions, 2D via pointers	decay.c
11	Dynamic Memory	malloc/calloc/realloc/free, ownership, leaks, use-after-free, growth strategy	heap.c

Part III — Building Things

#	Lesson	You will learn	Key file
12	Structs & Unions	Composite types, padding and alignment, ->, unions as tagged variants	structs.c
13	File I/O	fopen/fclose, text vs binary, fgets over gets, error-checking discipline	fileio.c
14	Preprocessor & Headers	Macros and their pitfalls, include guards, multi-file programs, static linkage	main.c
15	Function Pointers	Callbacks, qsort with your own comparator, dispatch tables	callbacks.c
16	Linked Structures	Singly linked list, stack, queue — built from scratch, freed correctly	list.c

---

Practice

Forty problems, sorted by difficulty. Every one ships with a reference solution — but the solution is a separate file, so you have to choose to look.

Tier	Problems	Sample
Beginner	15	FizzBuzz, prime sieve, temperature table, digit sum, palindrome check
Intermediate	15	Matrix multiply, binary search, string tokenizer, bit counting, Caesar cipher
Advanced	10	Dynamic array, hash table, memory pool, bitset, matrix determinant

cd practice/beginner
make             # build all fifteen solutions
./01_fizzbuzz    # run one
make run         # or run every solution in turn

---

Projects

Three programs worth putting on a résumé — each one real, self-contained C.

Project	What it is	Concepts pulled in
01 — Calculator	An RPN expression evaluator with its own stack	arrays, parsing, error handling
02 — Todo CLI	A task manager that persists to disk	dynamic memory, structs, file I/O
03 — Word Frequency	A hash-table word counter with sorted output	hashing, qsort, dynamic growth

---

Repository layout

C_educator/
├── lessons/              16 lessons, each a folder you can cd into
│   ├── 01-hello-world/       README.md + hello.c
│   ├── ...
│   └── 14-preprocessor/      README.md + main.c + mathutils.{c,h}
├── practice/            40 problems with reference solutions
│   ├── beginner/             15 · loops, arrays, strings
│   ├── intermediate/         15 · algorithms, bits, parsing
│   └── advanced/             10 · everything that calls malloc
├── projects/             3 complete programs
│   ├── 01-calculator/        RPN evaluator        calc.c
│   ├── 02-todo-cli/          persistent tasks     todo.c
│   └── 03-word-frequency/    hash-table counter   wordfreq.c
├── docs/                 setup · cheatsheet · UB traps · style · roadmap
├── .github/workflows/    CI: gcc + clang, sanitizers, valgrind
└── Makefile              builds and runs all 59 programs

---

Quality bar

Every .c file here is held to the same standard, and CI enforces it on every push:

gcc -std=c17 -Wall -Wextra -Wpedantic -Werror file.c -o file

• Zero warnings. Not "a few harmless ones" — zero. -Werror turns a warning into a build failure.
• Zero leaks. Anything that mallocs also frees, and the comment says who owns it.
• Every return value checked. malloc, fopen, fgets — all of them.
• Runs, not just compiles. CI executes each binary and fails on a non-zero exit.

make check builds all 59 programs and runs every one of them. The expected last line is all 59 programs exited 0.

If you find a file that violates any of these, that is a bug — please open an issue.

---

Reference material

Document	Contents
docs/SETUP.md	Getting a compiler on Linux, macOS and Windows
docs/CHEATSHEET.md	Format specifiers, operator precedence, <string.h> at a glance
docs/UB_TRAPS.md	Fourteen ways to invoke undefined behaviour, and how to avoid each
docs/STYLE_GUIDE.md	The conventions every file here follows
docs/ROADMAP.md	Where this curriculum goes next

---

How to actually learn from this

1. Read the lesson README first. It frames the problem before showing the code.
2. Type the example out. Do not copy-paste. Muscle memory is part of the point.
3. Break it deliberately. Remove an &, drop the free, index one past the end. Watch what the compiler says — and what it does not say.
4. Do the exercises before reading the solutions. A solution you read is worth roughly a tenth of a solution you wrote.
5. Move on before you feel ready. C rewards returning to a topic more than grinding it.

---

Contributing

New exercises, clearer explanations and bug reports are all welcome — see CONTRIBUTING.md.

License

MIT — use it, fork it, teach with it.

Start with Lesson 01 →