diff --git a/.gitignore b/.gitignore
index 9f97022..5f32e70 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
-target/
\ No newline at end of file
+target/
+.env
\ No newline at end of file
diff --git a/src/bin/02ca_strings.rs b/src/bin/02ca_strings.rs
index 2718120..64f8f43 100644
--- a/src/bin/02ca_strings.rs
+++ b/src/bin/02ca_strings.rs
@@ -1,5 +1,10 @@
+// Some Notes:
+// clones are expensive, since the data in the heap for the strings must be copied into another heap location
+// borrowed strings &str are fixed sized references to the underlying str data
+
 fn main() {
     let speech = "\"Ouch!\" said the well.\n";
+    // All Strings are the same size because they are simply the size of the Fat pointer pointing to some region in the heap memory
 
     println!("Speech: {speech}");
 
diff --git a/src/bin/0a_intro.rs b/src/bin/0a_intro.rs
index e7323d1..82799da 100644
--- a/src/bin/0a_intro.rs
+++ b/src/bin/0a_intro.rs
@@ -12,4 +12,14 @@ fn main() {
     the current directory the user must explicity specify the current directory
     as the path to check for the script
      */
+
+    let name = String::from("Brian");
+    println!("Outer {name}");
+
+    {
+        let name = String::from("Hello");
+        println!("Inner {name}");
+    }
+
+    println!("Outer {name}");
 }
diff --git a/src/bin/17bb_hashset.rs b/src/bin/17bb_hashset.rs
new file mode 100644
index 0000000..c06f432
--- /dev/null
+++ b/src/bin/17bb_hashset.rs
@@ -0,0 +1,13 @@
+use std::collections::{HashMap, HashSet};
+
+fn main() {
+    let mut _ages = HashMap::<String, String>::new();
+    let mut seen = HashSet::<&str>::new();
+
+    // the insert method on hashset returns a boolean indicating whethere the item was added or not
+    // the item is added when it's not already present in the hashset else is it not added
+    let _inserted = seen.insert("Brian");
+    let _inserted = seen.insert("Joseph");
+
+    let _ = _ages.keys();
+}
diff --git a/src/bin/22d_more_on_iterators.rs b/src/bin/22d_more_on_iterators.rs
new file mode 100644
index 0000000..7f59ed9
--- /dev/null
+++ b/src/bin/22d_more_on_iterators.rs
@@ -0,0 +1,27 @@
+fn main() {
+    let v = vec![1, 2, 3, 4, 5, 6];
+    let v_iter = v.iter();
+
+    for item in v_iter {
+        println!("Item: {item}")
+    }
+
+    for item in v {
+        println!("I: {item}");
+    }
+
+    // methods that call the next method in iterators are called consumers
+    // methods that do not call next method are called adapters
+    let sum_of_values = [1, 2, 3, 4, 5].iter().sum::<i32>();
+    println!("Sum of values = {sum_of_values}");
+
+    // after using a consumer, the iterator is well, CONSUMED
+    // adapters are methods that produce other iterators
+    // in this case, the map method is an adapter method
+    let _v2_iter = [2, 3, 4, 5].iter().map(|x| x * x).collect::<Vec<_>>();
+
+    // let sum_of_squares: i32 = v.iter()
+    //     .filter(|&x| x % 2 == 0)
+    //     .map(|x| x*x)
+    //     .sum();
+}
diff --git a/src/bin/45_strings_and_text.rs b/src/bin/45_strings_and_text.rs
index 0af9c16..7503511 100644
--- a/src/bin/45_strings_and_text.rs
+++ b/src/bin/45_strings_and_text.rs
@@ -1,4 +1,3 @@
-
 fn main() {
     // Rust treats strings as UTF-8 Encoded by default
     let s = "你好 Rust";
@@ -31,4 +30,3 @@ fn main() {
     // .is_ascii_alphabetic() ...
     //
 }
-
diff --git a/src/bin/48c_send_and_sync.rs b/src/bin/48c_send_and_sync.rs
new file mode 100644
index 0000000..ad2284c
--- /dev/null
+++ b/src/bin/48c_send_and_sync.rs
@@ -0,0 +1,31 @@
+use std::{sync::Arc, thread};
+
+fn main() {
+    // Send data types can be sent across thread
+    let string = String::from("Data");
+    let handle = thread::spawn(move || {
+        println!("{string}");
+    });
+
+    handle.join().unwrap();
+
+    // Sync data types can be referenced from multiple threads
+    // the Arc is placed on the heap and a reference count it maintained
+    let data = Arc::new(5);
+
+    let clone1 = Arc::clone(&data);
+    let clone2 = Arc::clone(&data);
+
+    let handle_2 = thread::spawn(move || {
+        println!("{}", clone1);
+    });
+
+    let handle_3 = thread::spawn(move || {
+        println!("{}", clone2);
+    });
+
+    handle_2.join().unwrap();
+    handle_3.join().unwrap();
+
+    // T is Sync if &T is Send
+}
diff --git a/src/bin/49_macros.rs b/src/bin/49_macros.rs
new file mode 100644
index 0000000..fe1d2be
--- /dev/null
+++ b/src/bin/49_macros.rs
@@ -0,0 +1,146 @@
+fn main() {
+    // an example of a macro is the assert_eq! macro
+    // this functionality could have been written as a generic function
+    // but macros do more than functions can do, for example, when an assert_eq! macro fails
+    // it prints the filename and the line number where the failure happened, fucntions have no way of getting that information
+
+    // macros are expanded during the compilation phase before types are checked and well before
+    // any machine code is generated, they are expanded recursively into rust code, since macros expansion
+    // can themselves contain macros
+    //
+    // macros are differentiated from functions with the bang symbol before their parenthesis
+    //
+    // macro_rules! macro is the main way to define macros in Rust
+    // when defining macros, the ! is not used, it is only used when calling them
+    // a macro defined by macro_rules works entirely by pattern matching
+    /*
+     * (pattern 1) => (template 1)
+     * (pattern 2) => (template 2)
+     *
+     */
+
+    // you can use square brackets or curly braces for macros, they are still work
+    println!("Hello");
+    println!["Hello"]; // this is why vec! is possible
+    println! {"Hello"};
+
+    // by convention, () are used for assert_*! macros, [] for vec! and {} for macro_rules!
+    // assert_eq! expands to
+    // assert_eq![2, 1 + 1];
+
+    /*
+    * match (&2, &(1 + 1)) {
+            (left_val, right_val) => {
+                if !(*left_val == *right_val) {
+                    let kind = ::core::panicking::AssertKind::Eq;
+                    ::core::panicking::assert_failed(
+                        kind,
+                        &*left_val,
+                        &*right_val,
+                        ::core::option::Option::None,
+                    );
+                }
+            }
+        };
+    */
+
+    macro_rules! answer {
+        () => {
+            42
+        };
+    }
+
+    macro_rules! double {
+        ($x:expr) => {
+            $x * 2
+        };
+    }
+
+    let result = double!(answer!());
+    println!("Result: {}", result);
+
+    // Some interestig macros
+    // file!() return a string path of the current file
+    // line!() return the line which the first macro that call it was called from
+    // column!() same as above, but for column
+    // include!("filename.rs"), includes the content of the file in the current line, the content must be valid Rust code
+    // include_str!("file.txt"), include the text content of the specified file
+    // include_bytes!("file.dat") same as above, but the file is treated a binary data
+    // todo!(), unimplemented!()
+    // matches!(value, pattern)
+
+    // Building the json! Macro
+    use std::collections::HashMap;
+
+    #[allow(dead_code)]
+    #[derive(Clone, PartialEq, Debug)]
+    enum Json {
+        Null,
+        Boolean(bool),
+        Number(f64),
+        String(String),
+        Array(Vec<Json>),
+        #[allow(clippy::box_collection)]
+        Object(Box<HashMap<String, Json>>),
+    }
+
+    macro_rules! json {
+          // the null literal must be matched directly
+          (null) => { Json::Null };
+          ([ $( $element:tt ),* ]) => { Json::Array(vec![ $( json!($element) ),* ]) };
+          ({ $( $key:tt : $value:tt ),* }) => { Json::Object(Box::new(vec![
+              $( ($key.to_string(), json!($value)) ),*
+          ])) };
+          ( $other:tt ) => {
+              Json::from($other)
+          }
+      }
+
+    impl From<bool> for Json {
+        fn from(b: bool) -> Json {
+            Json::Boolean(b)
+        }
+    }
+
+    impl From<String> for Json {
+        fn from(value: String) -> Json {
+            Json::String(value)
+        }
+    }
+
+    impl<'a> From<&'a str> for Json {
+        fn from(value: &'a str) -> Json {
+            Json::String(value.to_string())
+        }
+    }
+
+    macro_rules! impl_from_num_for_json {
+          ( $( $t:ident ),* ) => {
+              $(
+                impl From<$t> for Json {
+                    fn from(n: $t) -> Json {
+                        Json::Number(n as f64)
+                    }
+                }
+              )*
+          };
+      }
+
+    impl_from_num_for_json!(
+        u8, i8, u16, i16, u32, i32, u64, i64, u128, i128, usize, isize, f32, f64
+    );
+
+    assert_eq!(json!(null), Json::Null);
+
+    let macro_generated_array = json!([1, 2, 3, 4]);
+    let hand_coded_array = Json::Array(vec![
+        Json::Number(1.),
+        Json::Number(2.),
+        Json::Number(3.),
+        Json::Number(4.),
+    ]);
+
+    assert_eq!(macro_generated_array, hand_coded_array);
+
+    // Macros marked with #[macro_export] are automatically public to other modules
+}
diff --git a/src/bin/50_unsafe_code.rs b/src/bin/50_unsafe_code.rs
new file mode 100644
index 0000000..9744b8e
--- /dev/null
+++ b/src/bin/50_unsafe_code.rs
@@ -0,0 +1,14 @@
+macro_rules! capitalize {
+    ($a: expr) => {
+        let mut v: Vec<char> = $a.chars().collect();
+        v[0] = v[0].to_uppercase().nth(0).unwrap();
+        $a = v.into_iter().collect();
+    };
+}
+
+fn main() {
+    let mut name = String::from("test");
+    capitalize!(name);
+
+    println!("{name}");
+}
diff --git a/src/bin/51_environment_variables.rs b/src/bin/51_environment_variables.rs
new file mode 100644
index 0000000..df637f2
--- /dev/null
+++ b/src/bin/51_environment_variables.rs
@@ -0,0 +1,3 @@
+// const API_KEY: &'static str = env!("API_KEY");
+
+fn main() {}