C-lings

Small C exercises to get you used to reading and writing C code, inspired by Rustlings 🦀.

Recommended Resource

For a comprehensive and friendly guide to C, I recommend Beej's Guide to C Programming.

It covers everything from basics to pointers and memory management in a very readable style.

Setup

1. Clone this repo.

2. Make sure you have a C compiler installed (GCC or Clang).

   • On macOS/Linux, cc is usually available.
   • On Windows, you might need MinGW or WSL.

3. Run the runner:

   ./clings.py

How to use

The script will guide you through the exercises in order.

1. It will try to compile and run the current exercise.

2. If it fails, read the error output.

3. Open the file (e.g., exercises/01_variables/variables1.c) in your editor.

4. Fix the code.

5. The compiler will try to compile and run your code again.

Tips:

• You should open the termial in a vertical split for the fastest feedback loop.
• You can generally Ctrl/Cmd + Click to open the file in your editor.

Lesson Summary

Lesson	Topic	What You'll Learn
00	intro	Entry points, return types, and C comment rules.
01	variables	Declaration, initialization, and const correctness.
02	types	Overflow, casting, signed/unsigned pitfalls, and promotions.
03	fixed-width ints	Portable integer types and limit macros.
04	string literals	Printing and assigning string literals safely.
05	input parsing	Safe line reads with fgets and number parsing with sscanf.
06	simple structs	Defining structs and accessing members.
07	enums & typedefs	Enum usage and typedef for structs.
08	control flow	Switch fallthrough fixes and loop scoping.
09	error handling	errno/strerror diagnostics and return codes.
10	functions	Prototypes and pass-by-value vs reference patterns.
11	pointers	Address-of, dereference, and const pointer qualifiers.
12	pointer structs	Dot vs arrow operators with struct pointers.
13	arrays	Decay, bounds, checked access, and VLA parameters.
14	pointer arithmetic	Pointer increment and distance calculations.
15	string manipulation	Terminators, safe string APIs, and buffer sizing.
16	malloc/free	Heap allocation, leaks, and calloc vs malloc.
17	realloc	Resizing patterns and flexible array members.
18	memory layout	offsetof, padding math, and struct layout.
19	double pointers	Allocating for callers and 2D arrays.
20	command line args	argc/argv basics.
21	macros	Precedence, side effects, do-while, stringify, token pasting, variadics.
22	preprocessor	Conditional compilation and include guards.
23	files	fopen errors and binary/text IO.
24	unions & bitfields	Union memory sharing and bitmasking.
25	linkage	static, extern, and static local persistence.
26	function pointers	Callbacks, qsort, and void* patterns.
27	variadic functions	Building a variadic sum function.
28	undefined behavior	Dangling pointers, use-after-free, and shift UB.

Progress

Your progress is saved in .c-lings-state.txt. To reset, just delete that file.

License

MIT License.

Related Projects

• C-init: A tool to initialize a C project with everything you need to hit the ground running.