Notes on pointers.

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notes/_journal/2024-11-23.md

@@ -2,8 +2,11 @@
 title: "2024-11-23"
 ---
 
-- [ ] Anki Flashcards
+- [x] Anki Flashcards
 - [x] KoL
 - [x] OGS
 - [ ] Sheet Music (10 min.)
 - [ ] Korean (Read 1 Story)
+
+* Notes on Apostol's axiomatic definition of [[area]].
+* More notes on [[derived#Pointers|pointers]].

notes/algorithms/order-growth.md

@@ -440,7 +440,7 @@ END%%
 %%ANKI
 Basic
 What is the transpose symmetric property of $\Theta$-notation?
-Back: N/A
+Back: N/A.
 Reference: Thomas H. Cormen et al., Introduction to Algorithms, Fourth edition (Cambridge, Massachusett: The MIT Press, 2022).
 <!--ID: 1709752223322-->
 END%%

notes/c17/strings.md

@@ -136,6 +136,8 @@ Tags: printf
 <!--ID: 1708425941269-->
 END%%
 
+### Flags
+
 | Flag | Description                                                                                                                                                                                                                 |
 | ---- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | `-`  | Left-aligns the output                                                                                                                                                                                                      |
@@ -400,6 +402,8 @@ Tags: printf
 <!--ID: 1710673807990-->
 END%%
 
+### Length
+
 Length    | Description
 --------- | -----------
 `hh`      | `int` sized integer argument promoted from a `char`
@@ -457,6 +461,8 @@ Tags: printf
 <!--ID: 1708426673725-->
 END%%
 
+### Specifiers
+
 Specifier | Description
 --------- | -----------
 `d`, `i`  | a decimal `signed int`
@@ -960,6 +966,15 @@ Tags: printf
 <!--ID: 1707852083126-->
 END%%
 
+%%ANKI
+Basic
+What should be done to a pointer outputted by the `%p` format specifier?
+Back: It should be cast to a `void*` pointer.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+Tags: printf
+<!--ID: 1732397726966-->
+END%%
+
 %%ANKI
 Basic
 Given `int64_t x`, why is `printf("%d", x)` a problem?

notes/c17/typedefs.md

@@ -103,6 +103,40 @@ Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70
 <!--ID: 1730740461662-->
 END%%
 
+%%ANKI
+Basic
+When can two pointers be subtracted?
+Back: Only if both refer to elements of the same array object.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726963-->
+END%%
+
+%%ANKI
+Basic
+What is the result of `p - q` in the following?
+```c
+double A[4] = { 0.0, 1.0, 2.0, -3.0 };
+double* p = &A[1];
+double* q = &A[3];
+```
+Back: `-2`
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726964-->
+END%%
+
+%%ANKI
+Basic
+What is the result of `p - q` in the following?
+```c
+double A[4] = { 0.0, 1.0, 2.0, -3.0 };
+double* p = &A[3];
+double* q = &A[1];
+```
+Back: `2`
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726965-->
+END%%
+
 %%ANKI
 Basic
 Is `size_t` signed or unsigned?

notes/c17/types/derived.md

@@ -1133,6 +1133,143 @@ Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Program
 <!--ID: 1731942192229-->
 END%%
 
+%%ANKI
+Basic
+Trap representations are most relevant to what kind of derivied type?
+Back: Pointers.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726948-->
+END%%
+
+%%ANKI
+Basic
+What does a trap representation refer to?
+Back: An invalid interpretation of a bit pattern as a specific type.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726951-->
+END%%
+
+%%ANKI
+Basic
+What happens when accessing an object with a trap representation of its type?
+Back: Undefined behavior.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726952-->
+END%%
+
+%%ANKI
+Basic
+*Why* must a dereferenced object have the correct designated type?
+Back: A trap representation of an object's type leads to undefined behavior.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726953-->
+END%%
+
+%%ANKI
+Basic
+Refer to the following. *Why* isn't the pointer addition considered correct?
+```c
+double A[2] = { 0.0, 1.0 };
+double* p = &A[0] + 2;
+```
+Back: N/A. It is.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726954-->
+END%%
+
+%%ANKI
+Basic
+Refer to the following. *Why* isn't the pointer addition considered correct?
+```c
+double A[2] = { 0.0, 1.0 };
+double* p = &A[0] + 3;
+```
+Back: Pointers cannot refer to addresses beyond that immediately following the array.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726955-->
+END%%
+
+%%ANKI
+Basic
+Refer to the following. What values of `N` yield a valid pointer assignment?
+```c
+double A[2] = { 0.0, 1.0 };
+double* p = &A[N];
+```
+Back: `0`, `1`, and `2`.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726956-->
+END%%
+
+%%ANKI
+Basic
+Refer to the following. What is the first value of `N` that yields an invalid pointer assignment?
+```c
+double A[2] = { 0.0, 1.0 };
+double* p = &A[N];
+```
+Back: `3`
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726957-->
+END%%
+
+%%ANKI
+Basic
+Refer to the following. Is the last line a valid dereference?
+```c
+double A[2] = { 0.0, 1.0 };
+double a = *(&A[1]);
+```
+Back: Yes.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726958-->
+END%%
+
+%%ANKI
+Basic
+Refer to the following. Is the last line a valid dereference?
+```c
+double A[2] = { 0.0, 1.0 };
+double a = *(&A[2]);
+```
+Back: No.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726959-->
+END%%
+
+%%ANKI
+Cloze
+A pointer must point to a {valid object}, or {one position beyond} a valid object, or be {null}.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726960-->
+END%%
+
+%%ANKI
+Basic
+Consider the following. At what point *could* the program crash?
+```c
+double A[] = { 0.0, 1.0 };
+double* p = &A[0] + 2;
+double q = *p;
+```
+Back: On the third line.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726961-->
+END%%
+
+%%ANKI
+Basic
+Consider the following. At what point *could* the program crash?
+```c
+double A[] = { 0.0, 1.0 };
+double* p = &A[0] + 3;
+double q = *p;
+```
+Back: On the second line.
+Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
+<!--ID: 1732397726962-->
+END%%
+
 ## Bibliography
 
 * Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.

notes/geometry/index.md

@@ -1,5 +1,9 @@
 ---
 title: Geometry
+TARGET DECK: Obsidian::STEM
+FILE TAGS: geometry
+tags:
+  - geometry
 ---
 
 ## Overview