Memorize C Pointers, Memory and Syntax: 75 Flashcards on malloc, Dangling Pointers and Undefined Behavior

Most C decks teach syntax. Deck AW7614 spends its 75 cards on the part that actually breaks programs: what a pointer holds, who owns the memory, and which perfectly compilable line is undefined behaviour. If you can already write a for-loop but still hesitate before free(), this is the deck.

How the 75 cards are laid out

Cards 1-4 are spec-sheet trivia (successor to B, multi-paradigm, "static, weak, manifest, nominal" typing). Cards 5-20 are the core: pointers, &, NULL, malloc/calloc/realloc/free, leaks, dangling pointers, array decay. Cards 21-31 cover aggregates and the entry point, 32-49 the preprocessor and the qualifiers, 50-61 control flow and undefined behaviour, 62-75 the standard library and null-terminated strings.

Everything the deck makes you recall

Address-of and dereference operators, sizeof, null pointers, function pointers and their declaration syntax; malloc, calloc, realloc, free, memory leaks, dangling pointers, segmentation faults, buffer overflows, the absence of bounds checking; struct, union, enum, typedef, dot versus arrow access, _Bool and stdbool.h; static, extern, const, volatile, register; #include, #define, #ifdef, angle brackets versus quotes; argc, argv, both legal main signatures; printf, scanf, strcpy, strncpy, strlen, the \0 terminator, ternary and comma operators, prefix versus postfix increment.

Fix the capitalisation before you memorise it

Nine fronts are sentence-cased by the deck's generator: Sizeof, Argc, Argv, Printf, Scanf, Malloc, Realloc, Strcpy, Strlen. In C every one of those is lowercase, and Printf will not compile. Read the capital as a formatting artefact, never as the identifier. Four of the same cards also lost their opening question — Main function, Switch statement, Malloc, Strlen all have answers ("An int value…", "NULL - always check the return value…") that only parse as what does X return / take? Restore the question mentally and they work as fill-in-the-blank prompts.

Two backs to correct, one drill to add

Card 74 says strings are passed "by reference", which contradicts card 32 and the language itself: C has no pass-by-reference. The pointer is copied by value — that is exactly why &variable is needed to modify a caller's data. And strncpy is sold as the safer alternative to strcpy; it is not, because it silently omits the null terminator when the source fills the buffer. Prefer snprintf, which the same card also lists. (Minor: card 39 announces "three comment styles" and supplies two.)

The drill: answer every pointer card with a drawing, not a sentence. Two boxes, one arrow, the address written inside. Array decay, ptr+1, dangling pointers and char* const all become obvious in that notation and stay ambiguous in prose.

Deck AW7614 — C: Pointers, Memory & Syntax is in the Flip It library at flip-it.app. Coming from a managed language? The contrast with C# and .NET Core — garbage collection, boxing, the CLR — makes both decks stick faster.