tweaks to C notes

zk/Char_data_type_in_C.md

@@ -60,30 +60,17 @@ In memory this would actually be:
 With each char corresponding to an ASCII number apart from the null which would
 just be `0000 0000`.
 
-### String literals
-
-The easiest way to declare a string as a `char` array is to use the format we've
-already used which is string literal notation:
-
-```c
-char word[] = "Hello";
-```
-
-The null terminator is implied in this form, you do not need to add it manually.
-Also the length is fixed to the length of the string (in this case `6` for the
-five actual characters plus the null).
-
-### Non-literal string declaration
-
 The more formal way of doing this would be:
 
 ```c
 char word[6] = {'H', 'e', 'l', 'l', 'o', '\0'}
 ```
 
-However, in practice, if you just want quick access to a string, where you don't
-need to modify the individual characters later, you can just use a direct
-pointer definition:
+### String literals
+
+In practice, if you just want quick access to a string, where you don't need to
+modify the individual characters later, you can just use a direct pointer
+definition:
 
 ```c
 char *name = "Thomas";
@@ -94,3 +81,15 @@ is a string literal and is stored as read-only. It can be redefined (the pointer
 can point to something else) but it's not mutable itself.
 
 More info in [Pointers in C](./Pointers_in_C.md).
+
+Note that the `*` in the declaration is part of the type definition, it's
+signalling that its a pointer to a string literal, it's not
+referencing/dereferencing or doing anything to the bytes.
+
+Technically you could write:
+
+```c
+char* name = "Thomas"
+```
+
+This would be clearer but it is not the convention.

zk/Macros_in_C.md

@@ -3,14 +3,35 @@ tags:
   - C
 ---
 
-Think of them as a find and replace that takes place before compilation.
+Think of macros as a find and replace that takes place before compilation at the
+[pre-processor](./C_compilation_process.md) stage.
 
-They are ephemeral and never make it into the compiled code.
+They are ephemeral and never make it into the compiled code in the form they are
+defined as.
 
-With a macro, the computation happens "inline" without having to call functions
-which make costly alterations to the stack.
+When the preprocessor injects the value, the injection happens "inline" without
+having to call functions which make costly alterations to the stack, which is
+the main benefit - efficiency.
 
-A function and function call such as:
+Starting with a simple example:
+
+```c
+#define NAME "Thomas"
+```
+
+This is not actually a variable because it has no memory address. It never makes
+it to memory-assignation because it doesn't exist after pre-processing. By the
+compilation stage,j this value has been added to the code as a type
+corresponding to the literal you defined; in this case a string literal
+(`char *`). To emphasise, the macro itself has no type because it doesn't exist
+at the type level (compilation), the data type it represents after injection is
+applied by the compiler through parsing.
+
+> The convention is to have macros in `ALL_CAPS` to distinguish them from real
+> variables. Don't confuse them for constants, constants are actually written in
+> lowercase like other actual variables.
+
+To use a more complex example, a function and function call such as:
 
 ```c
 int square(int x) { return x * x; }
@@ -32,7 +53,3 @@ int a = ((5) * (5));
 ```
 
 after pre-processing but before compilation.
-
-## Syntax
-
-`#define` always creates a macro but there are different types.

zk/Pointers_in_C.md

@@ -48,13 +48,17 @@ char *name = "Thomas";
 ```
 
 Then to reference the value (_not_ the address, the actual value) you just use
-`name`.
+`name`. The `*` is just part of the type definition in the above - it's just
+signalling the type. If you later want to change the value, you then use `*` as
+an operator:
 
-This is confusing but I just have to accept for now.
+```c
+*name = 'Tom';
+```
 
-Note that if you do this, it creates the string in read-only memory. You can't
-modify the individual characters of `"Thomas"`. To do this you would need to
-define it as:
+Note that if you use a pointer to `char`, it creates the string in read-only
+memory. You can't modify the individual characters of `"Thomas"`. To do this you
+would need to define it as:
 
 ```c
 char name[] = "Thomas";
@@ -85,6 +89,3 @@ Or, using a variable:
 static char *topic = "test_topic";
 mqtt_publish(mqtt_client, topic, "Test message");
 ```
-
-> Note in the above the `*` is part of the type definition, _not_ the variable.
-> Even more confusing!