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STUDENT NOTES · C & C++ WEEK 5 OF 8
Renting Memory & Keeping Records 🧠
Arrays have fixed sizes — but what if you don't know the size until runtime? Time to RENT memory… and always return it.
1malloc — renting memory at runtime
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Chip: malloc rents you raw bytes from the heap and hands back a POINTER (Week 4 pays off!). You choose the size while the program runs.
2free — ALWAYS return what you rent
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Bugly: Rent memory in a loop and never free it? The program eats RAM until the machine begs for mercy. A memory leak — my slowest, cruelest attack. Hehehe.
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Professor Hoot: Golden rule: every malloc has a matching free. Python's garbage collector spoiled you — in C, YOU are the garbage collector.
3Files in C
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Chip: Same ideas as Python's Day 13 — "w" writes, "r" reads, "a" appends — with fopen/fclose doing the ceremony. And ALWAYS check for NULL: the file might not exist.
4Sorting sets up searching
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Bittu: Binary search finds 1 number among a MILLION in ~20 looks — but only on a SORTED array. Sort first, search fast. Class covers the classic sorts live.
5Quick quiz! 🧠
You malloc memory in a loop and never call free. What happens?
💡 Nothing frees itself in C. Leaks build until the OS steps in. Every malloc needs its free.
fopen("data.txt", "r") on a missing file returns…
💡 Read mode needs the file to exist; on failure fopen returns NULL. Dereference NULL and… segfault city.
6Your mission 🚀
Mission 1: malloc space for 5 ints, fill them with squares (1,4,9,16,25), print, then free.
Mission 2: Write your 3 favourite games to games.txt with fprintf, then read them back with fgets.
Mission 3: Open a file that doesn't exist and print a friendly message when fopen gives NULL.
Week 5 complete — Month 1 of C conquered! 🏆
Next: C++ enters — classes, objects and cout. Same engine, shinier body.
Go to Week 6: Hello C++ →