finished ch3 started on ch4

data_types.md

@@ -120,6 +120,13 @@ value stored 13
     let l = 0b1101;
 ```
 
+##### Bytes
+u8 only
+value stored 0x41 or 65
+```rust
+    let m = b'A';
+```
+
 ## Numeric Operators / Basic Math
 Numbers for reference
 ```rust
@@ -158,8 +165,8 @@ Numbers for reference
 must be explicity typed to true or false
 0 or 1 not allowed even with let var: bool
 ```rust
-    let m = false;
-    let n = true;
+    let n = false;
+    let o = true;
 ```
 
 ### Char
@@ -167,8 +174,111 @@ must use single quotes and not "" otherwise will be inferred as string literal
 is stored as Unicode Scalar Value allowing for emoji, japanse char and other languages not supported by ASCII
 takes 4 bytes in size or 32 bits
 ```rust
-    let o = 'a';
+    let p = 'a';
 ```
 
-### Compound Types
+## Compound Types
+multiple values into one type
 
+### Tuple
+A general way of grouping multiple a number of values into one compound type
+types do not need to be the same in every position
+
+```rust
+    let tup: (i32, f64, u8) = (500, 6.4, 1);
+```
+The variable tup has values written to it at initialization but it is not requried, order does not matter
+similar to a struct in c
+
+Vaules must be destructed out of a tuple to be accessed inidivually, can use a pattern matching to the tuple
+
+```rust
+ let (q, r, s) = tup;
+```
+
+This is called destructing becasue it breaks it into 3 parts
+
+Can also be accessed with a .
+
+***INDEX STARTS AT 0***
+```rust
+    let t = tup.0;  // t = 500
+    let u = tup.1;  // u = 6.4
+    let v = tup.2;  // v = 1
+```
+
+#### A Unit
+
+This is a special value where a tuple has no values
+```rust
+    let w: () = ();
+```
+This represents an empty type or an empty return type
+
+Expressions will implicitly return a unit if they dont return anything else
+
+### Array
+
+A collection of multiple values
+Must have every value be the same type, cannot mix and match
+Arrays must be a fixed length at initialization
+useful when you want a set number of values or is static
+
+Values are in [] and seperated by ,
+
+```rust
+    let xa = [1, 2, 3, 4, 5, 6];
+```
+
+Array located in stack same with above types
+
+If you need your array/list to grow or shrink use a vector
+If unsure weather to use an Array or Vector pick a vector
+
+Times where using an array is better
+```rust
+let months = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];
+```
+
+Accessing items in an array
+```rust
+    let ya = xa[0]; //value is 1
+```
+
+Initializing an Array
+```rust
+    let za: [i32; 5];   // allows for 5 32 bit signed integers inside
+    let aa = [i8; 6];   // allow for 6 8 bit signed integers inside
+```
+
+Invalid Array Elements
+
+```rust
+use std::io;
+fn main() {
+    let a = [1, 2, 3, 4, 5];
+
+    // Input of a number
+    println!("Please enter an array index.");
+    let mut index = String::new();
+    io::stdin()
+        .read_line(&mut index)
+        .expect("Failed to read line");
+
+    // change into a integer
+    let index: usize = index
+        .trim()
+        .parse()
+        .expect("Index entered was not a number");
+
+    // access elemetn in array
+    let element = a[index];
+    println!("The value of the element at index {index} is: {element}");
+}
+```
+this program would compile with not problems
+for example inputting 7 into the program
+this would cause a runtime error
+the program would output an error because it didnt get to the final line println! before exiting 
+it casue the program to exit before attempting to access the invalid space
+this is a form of safe memory management that rust name