more C notes

zk/Booleans_in_C.md

@@ -0,0 +1,44 @@
+---
+tags:
+  - C
+---
+
+Booleans are a bit weird in C. _Oficially_ they don't exist as a core primitive
+data type. Instead you use integers on the basis that:
+
+> `0` is false and any non-zero value is true (but typically indicated with `1`)
+
+Hence why the `int main()` [entrypoint](./Entry_point_to_C_programs.md) returns
+`int`, because "success" is `1` and "error" is `0`.
+
+A common example of this approach:
+
+```c
+
+int is_running = 1; // true
+int has_error = 0; // false
+
+if (is_running) {
+    // Do stuff
+}
+
+```
+
+Since the **C99** standard, a dedicated Boolean type has been available.
+
+```c
+#include <stdbool.h>
+
+bool is_running = true;
+bool has_error = false;
+
+if (is_running) {
+     // Do stuff
+}
+```
+
+Note, you must include the bool header file which is part of the core in order
+to have access to the `bool`, `true`, and `false` keywords.
+
+This is just syntactic sugar though, and underneath it is just `int` values for
+`0` and `1`.

zk/C_is_call_by_value.md

@@ -1,3 +1,8 @@
+---
+tags:
+  - C
+---
+
 When you pass a value into a C function as an argument it creates a copy of the
 value that is stored outside of the function (the parameter value). This value
 is modified by the function.
@@ -59,6 +64,3 @@ Which will cause the main function to return what we expect:
 ```txt
 a = 17, b = 21
 ```
-
-While the non-pointerized version of the function enshrines **call by value**,
-the pointerized version enshrines **call by reference**.

zk/Pointers_in_C.md

@@ -6,59 +6,34 @@ tags:
 A pointer is a reference to the address of a variable in memory.
 
 ```c
-int num = 27;
+int x = 27;
-int *ptr_to_num = #
+int *ptr = &x;
 
-printf("%i\n", num);
+printf("%i\n", x);
 // 27
 
 
-printf("%p\n", ptr_to_num);
+printf("%p\n", *ptr);
 // 0x7ffeb44f7eac
 ```
 
-We indicate that we are creating a pointer with `*`.
+The `&` and `*` is frankly confusing.
 
-We then retrieve the memory address with `&`.
+In the previous example, `int *ptr = &x`, `ptr` is a variable that holds the
+memory address of `x`. `*` signals that it is a pointer variable, `&` is what
+does the retrieval.
 
-We can 'de-reference' back to the value with:
+In the following:
 
 ```c
-printf("%i\n", *ptr_to_num);
+int x = 27;
-// 27
+int *ptr = &x;
+int value = *ptr;
 ```
 
-## Why are pointers even necessary?
+We again set `ptr` to the memory address of `x`, but we use `*` on the last line
+to **de-reference** the pointer and get the original value back. Thus `value`
+becomes equal to `27`.
 
-In other languages you can do something like:
+Pointers are necessary because C uses a [call by value](./C_is_call_by_value.md)
-
+system for function arguments.
-```js
-let num = 27;
-console.log(num);
-// 27
-
-function modify(theNumber) {
-  theNumber = 28;
-  return theNumber;
-}
-```
-
-In C, you cannot use functions to modify variables that live outside of them
-(e.g. in higher scope).
-
-If you did the above with C, `num` would still be `27` after the function call.
-This is bcause arguments are passed by value, not by reference to the item in
-memory that the variable refers to.
-
-So, to modify the actual value in memory, you invoke pointers.
-
-The above JavaScript in C would be:
-
-```c
-int num = 27
-
-int modify(int *the_number) {
-    *the_number = 28;
-    return the_number;
-}
-```