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FollowtheDamnCode

C from zero

Learn to program from zero with C — the language underneath almost everything. You'll see exactly how code, memory, and the machine fit together, which makes every language after it easier. The whole course is free.

1Getting Started

What a program is, and your first one running.

  1. What Is a Program?Instructions for a computer — and why we start with C.
  2. Your First C Programmain(), printf, and running real code.
  3. CommentsNotes in your code that the computer ignores.

2Variables & Data

Storing values, printing them, and reading them from the user.

  1. VariablesA named box that stores a value.
  2. Data Typesint, float, and char — whole numbers, decimals, and letters.
  3. How Big Is a Variable? (sizeof)Every type takes up a fixed amount of memory.
  4. Constants and KeywordsValues that never change, and words C reserves for itself.
  5. Printing with printfFormat codes and escape sequences like \n and \t.
  6. Taking Input with scanfReading numbers the user types.

3Operators

Doing math and combining values.

  1. Arithmetic Operators+, -, *, /, and % (remainder).
  2. Type Conversion and CastingWhy 5 / 2 is 2, and how to get 2.5.
  3. Operator PrecedenceWhich operation happens first.
  4. Bitwise OperatorsWorking on the 0s and 1s inside a number.

4Making Decisions

Running different code depending on a condition.

  1. if and elseDo one thing or another.
  2. Comparing and Combining Conditions==, <, >, &&, ||, and !.
  3. else ifChoosing between many options.
  4. The Ternary OperatorA one-line if-else.
  5. switchPicking one case out of many.

5Loops

Repeating code without writing it again.

  1. The while LoopRepeat while a condition is true.
  2. The do-while LoopRun once, then keep repeating.
  3. The for LoopRepeat a set number of times.
  4. Increment and Decrementi++, i--, ++i, and --i.
  5. break and continueLeave a loop early, or skip one round.

6Functions

Naming a piece of code so you can reuse it.

  1. FunctionsWrite code once, use it many times.
  2. Parameters and Return ValuesPassing values in and getting a result back.
  3. RecursionA function that calls itself.
  4. Scope and Storage ClassesWhere a variable can be seen, and how long it lives.

7Pointers

Variables that store where other variables live. Direct access to memory — with great power comes great responsibility.

  1. What Is a Pointer?An address, & to get it, * to follow it.
  2. Pointer to a PointerA pointer that points to another pointer.
  3. Call by Value vs Call by ReferenceWhy a swap function needs pointers.

8Arrays

Many values of the same type, in a row.

  1. ArraysA row of boxes under one name.
  2. Arrays and PointersMoving through an array with a pointer.
  3. 2D ArraysRows and columns, like a table.

9Strings

Working with text.

  1. StringsText is an array of characters ending in \0.
  2. Reading StringsGetting a word or a line from the user.
  3. String Functionsstrlen, strcpy, strcat, and strcmp.

10Structures

Grouping related values into your own type.

  1. StructuresOne variable that holds several related values.
  2. Arrays of Structures and Pointers to StructuresMany records, and the -> operator.
  3. typedefGiving a type a shorter name.
  4. EnumsNames for a fixed set of choices.
  5. UnionsSeveral members sharing one piece of memory.

11Working with Files

Saving data so it's still there next time.

  1. Opening and Closing Filesfopen, fclose, and file modes.
  2. Reading and Writing Filesfprintf, fscanf, fgetc, and fputc.

12Dynamic Memory

Asking for memory while the program runs — and the responsibility that comes with it: everything you take, you give back.

  1. malloc and callocGetting memory when you need it.
  2. free and reallocGiving memory back, and resizing it.

13Going Further

The tools real C programs lean on — read-only promises, functions as values, the preprocessor, many files, arguments, and the standard maths and clock.

  1. Const CorrectnessPromising not to change what you only read.
  2. Function Pointers and CallbacksPassing "which function to call" as a value.
  3. The Preprocessor and Macros#include, #define, include guards, and #if.
  4. Multi-File Programs and HeadersSplitting a program into modules with .h and .c files.
  5. Command-Line Argumentsargc, argv, and reading words typed after the program's name.
  6. Math, Random Numbers, and Timemath.h, rand and srand, and the clock.

14Writing Robust Code

Handling failure on purpose, and finding bugs when they happen anyway.

  1. Error Handling and Input ValidationReturn codes, errno, NULL checks, and never trusting input.
  2. DebuggingReading compiler errors, printf debugging, and the bugs C won't catch for you.

15Building Data Structures

Putting structs, pointers, and the heap together to build containers of your own.

  1. Dynamic ArraysA growable vector built on realloc.
  2. Linked ListsA chain of malloc'd nodes — the capstone of pointers and the heap.

16C Reference

Look-it-up pages: every keyword, the operator precedence table, printf/scanf format codes, and the most-used functions of the standard headers — each with its signature, a gotcha, and a tiny example.

  1. Reference: KeywordsEvery C keyword, grouped by what it's for.
  2. Reference: Operators and PrecedenceAll the operators, highest precedence first, with the classic traps.
  3. Reference: Format Specifiersprintf and scanf codes, widths, precision, and flags.
  4. Reference: stdio.hprintf, scanf, fgets, files, and friends.
  5. Reference: stdlib.hMemory, conversions, random numbers, qsort, and exit.
  6. Reference: string.hLength, copying, comparing, searching, splitting, and raw memory.
  7. Reference: math.hRoots, powers, rounding, logs, and trigonometry.
  8. Reference: ctype.hTesting and converting single characters.
  9. Reference: time.hThe clock, the calendar, strftime, and timing code.