notes on C

zk/Arrays_in_C.md

@@ -0,0 +1,41 @@
+---
+tags:
+  - C
+---
+
+# Arrays in C
+
+To declare an array in C, you must specify:
+
+- the data type of the variables it will store
+- the size (in square brackets)
+- the array elements (in curly brackets)
+
+Thus:
+
+```c
+int some_numbers[3] = {1, 2, 3};
+```
+
+> Array element individuation is the same as JavaScript, as is a standard `for`
+> loop.
+
+## Calculating the length of an array
+
+Determining the length of an array is a fairly involved process compared to
+higher-level languages. The process:
+
+- Get the size of the array **in bytes**
+- Divide this by the size of the first array element
+
+So:
+
+```c
+int some_numbers[3] = {1, 2, 3};
+int length = sizeof(some_numbers) / sizeof(arr[0]) // 3
+```
+
+What is happening under the hood:
+
+The array has three `int` values. The normal byte size for a single `int` is 4
+bytes (32 bits). 4 x 3 is 12. 12/4 is 3.

zk/Char_data_type_in_C.md

@@ -0,0 +1,83 @@
+---
+tags:
+  - C
+---
+
+# The `char` data type in C
+
+> A `char` is simply a 1-byte integer type that happens to be commonly used for
+> storing characters
+
+Don't get fixated on `char` _designating a character_. While it is mostly used
+for this, it is better understood as the _smallest integer type_ C provides (1
+byte). As C is so low-level there is a closer connection to data types just
+being binary numbers. Hence `h`, `!` and `6` are all stored as 8-bit binary
+numbers.
+
+As `char` uses 8 bits, you can represent/encode $2^8$ values (256).
+
+A _signed_ char (which is the default in C) allows for negative values hence it
+can be used to [encode](./Binary_encoding.md) the numbers -128 - 127.
+
+An _unsigned_ char gives you a greater positive range, 0 - 255.
+
+Now, when you actually want to store a textual character, the number
+corresponding to the `char` is looked up in the
+[ASCII](./Binary_encoding_of_text.md) table, e.g. `65` would be `A`.
+
+This is the only difference. In both cases a `char` is an 8-bit number, it's
+just with actual characters, you are running it through ASCII.
+
+This can be demonstrated by using the format specifiers for `char` and `int`
+against a `char`:
+
+```c
+char a_char = 65;
+printf("%i\n", aChar) // 65
+print("%c\n", aChar) // A
+```
+
+## Strings
+
+Unlike higher-level languges like Python, there is no independent string type in
+C: **strings are just arrays of `char`**.
+
+In order for the array of `char` to be understood as a string, the convention is
+to apply a null terminator ('\0') as the final element.
+
+Thus the string 'Thomas' would be declared:
+
+```c
+char name[] = "Thomas"
+```
+
+In memory this would actually be:
+
+```
+'T' 'h' 'o' 'm' 'a' 's' '\0'
+```
+
+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'}
+```

zk/Entry_point_to_C_programs.md

@@ -0,0 +1,25 @@
+---
+tags:
+  - C
+---
+
+# Entry point to C programs
+
+```c
+int main(void)
+{
+    // Instructions
+}
+```
+
+The braces wrap all code that comprises the program.
+
+The return type is `int`. It receives no arguments so the arguments are `void`.
+
+## Why does it return an `int`?
+
+It returns an `int` because the main function returns a success code: `0` for
+success and `1` for error.
+
+As C was divised to create Unix, this fits in with other Unix-like OS behaviour
+such as bash scripts returning `0`/`1`.

zk/Format_specifiers_in_C.md

@@ -7,15 +7,21 @@ created: Thursday, February 29, 2024 | 17:41
 
 # Format specifiers in C
 
-Format specifiers define the type of data to be printed on standard output. You
+Format specifiers define the type of data to be printed or interpolated in
-need to use format specifiers whenever you are
+standard output. You need to use format specifiers whenever you are
-[printing-values-in-c](printing-values-in-c.md).
+[printing values in C](./Printing_values_in_C.md).
+
+For example:
+
+```c
+int age = 37
+printf("My age is %i", age)
+```
 
 | Specifier | Usage   |
-| --------- | -------------------------- |
+| --------- | ------- |
-| `%c`      | single character           |
+| `%c`      | char    |
 | `%s`      | string  |
 | `%n`      | nothing |
-| `%d`      | integer (assuming base 10) |
+| `%i`      | integer |
 | `%f`      | float   |
-| `%%`      | The percent sign itself    |

zk/Variables_in_C.md

@@ -1,11 +0,0 @@
----
-id: r4i16p1x
-tags: [C]
-created: Thursday, February 29, 2024 | 17:20
----
-
-# Variables in C
-
-```c
-int age = 25
-```