Added notes on C

c.md

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+c -- C Programming Language
+===========================
+
+C has inspired various other languages.
+Languages that are extensions of C include C++ and Objective-C.
+
+Major interpreters and virtual machines written in C:
+- CPython (Python)
+- Ruby MRI (Ruby)
+- Zend Engine (PHP)
+
+Major operating systems written in C:
+- Unix
+- BSD
+- Linux
+- Windows
+- Darwin (Mac OS X, iOS)
+
+Major systems writtin in C:
+- Postgres
+- Redis
+- Memcached
+- Nginx
+- Apache
+
+You really should know C.
+I recommend learning C before C++ or Objective-C.
+
+## Memory
+
+Memory management is what makes C (and C++) a significantly different beast.
+Precautions must be taken, even by programmers transitioning from C++.
+
+- `&` is "address of" -- use on variable to get its memory address
+- `*` is "dereference" -- use on pointer variable to get/set value
+- `->` is "access member" -- use with struct/union to access member variable. Recall that it is sugar for dotting into dereferenced variable
+
+Use `malloc` to dynamically allocate memory _on the heap_:
+- e.g. `int* integers = (int*) malloc(sizeof(int) * 10);`
+- only argument is the number of bytes to allocate
+- calculate bytes by multiplying `sizeof` data type by number of that data
+  - e.g. `sizeof(int) * 10` for an integer array of 10
+- returns `void*` (void pointer) which you should cast
+- remember it DOES NOT initialize the array
+- remember to deallocate memory using `free` function
+- remember to set pointer to `NULL` after freeing memory
+
+## REFERENCES
+
+[C dynamic memory allocation](https://en.wikipedia.org/wiki/C_dynamic_memory_allocation). Wikipedia.
+
+[Dangling pointer](https://en.wikipedia.org/wiki/Dangling_pointer) Wikipedia.
+
+[malloc](http://man7.org/linux/man-pages/man3/malloc.3.html). Linux man page. Covers `malloc`, `free`, `calloc`, `realloc`.
+
+[Troubleshooting Segmentation Violations/Faults](http://web.mit.edu/10.001/Web/Tips/tips_on_segmentation.html)