pointers in C

zk/Arrays_in_C.md

@@ -3,8 +3,6 @@ tags:
   - C
 ---
 
-# Arrays in C
-
 To declare an array in C, you must specify:
 
 - the data type of the variables it will store

zk/Format_specifiers_in_C.md

@@ -14,6 +14,7 @@ created: Thursday, February 29, 2024 | 17:41
 | `%n`      | nothing |
 | `%i`      | integer |
 | `%f`      | float   |
+| `%p`      | pointer |
 
 Format specifiers define the type of data to be printed or interpolated in
 standard output. You need to use format specifiers whenever you are

zk/Pointers_in_C.md

@@ -0,0 +1,64 @@
+---
+tags:
+  - C
+---
+
+A pointer is a reference to the address of a variable in memory.
+
+```c
+int num = 27;
+int *ptr_to_num = #
+
+printf("%i\n", num);
+// 27
+
+
+printf("%p\n", ptr_to_num);
+// 0x7ffeb44f7eac
+```
+
+We indicate that we are creating a pointer with `*`.
+
+We then retrieve the memory address with `&`.
+
+We can 'de-reference' back to the value with:
+
+```c
+printf("%i\n", *ptr_to_num);
+// 27
+```
+
+## Why are pointers even necessary?
+
+In other languages you can do something like:
+
+```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;
+}
+```