monsalvogeoffrey / advent-of-code-2021-c

I'm using Advent of Code 2021 as exercices to learn and practice programming in C

In Advent of Code, each day contain two puzzles, the second one being a harder version of the first one, for a total of 50 puzzles of increasing difficulty.

In this repository, I'll list all of my working code in the format X-Y.c, with X being the day and Y being which of the day's challenge it's corresponding to. And X-Y.txt being the input.

What I've learned through this challenge.

Day 1, Challenge 1:

• Opening and reading a file
• atoi() for string to int converstion

Day 1, Challenge 2:

• Importing custom header files (Using it for qol.h, a set of typedef and macros that make C more comfortable for me)

At this point I decided to write a Makefile to compile/cleanup everything at once. make will compile everything make clean will delete every .exe file It's unnecessary, but I learned how Makefile works recently so that's good practice.

Day 2, Challenge 1:

• Dealing with strings is horrible !!!
• strcmp for string comparaison (return 0 if true)
• strtok for string spliting (/!\ DESTRUCTIVE, returns a pointer)
• typedef char string[]; isn't that helpful to deal with strings, C has an obsession with having to know the length in advance
• Riiiight, switch don't work on strings
• strcpy is necessary to extract the value of a pointer to a string (Since strings are just array of characters, the pointer actually only points to the first character, the function strcpy probably loop over the pointer and the next elements until it find a null byte)

Day 3, Challenge 1:

• How to do exponents
• Think of using the example as a test case
• int myVar[MY_CONST] = {0}; can be used to have an array of size that depends on a constant (macro) value

Day 3, Challenge 2:

• Implementing Vectors (simplified and only supports values of static sizes)
• A lot of dynamic memory allocation
• malloc(size_in_byte) to initilize what basically works as a manually mangaged array
• void* pointers will support any type of data
• Cast to char* to access individual bytes
• Do not forget to free memory, ideally if you have a struct that contain dynamically allocated properties, have a function that free them all at once
• fprintf() can print to stderr (or files)
• Just because a struct contains a dynamically allocated property doesn't make the struct itself have a dynamic size, the property in question is just a pointer, which itself is of static size
• memcpy(destination address, address to pull from, length to pull) from string.h to copy a continuous block of data
• Return NULL to indicate an error since C doesn't support raise() or throw() (I didn't diligently apply that)
• The inline keyword is annoying to work with and most of the time better avoided
• realloc(pointer, new size) only move the data, don't forget to re-assing the pointer
• struct->property translate to (*struct)->property as a shorthand to pull data from a pointer to a struct
• strtol(string, pointer to endpointer, base) to parse number of non-10 base
• C don't have ternary opperator
• Do not forget, when you do a for loop backward and your condition is i >= 0.... don't use an unsigned number