finished ch4

ownership/src/main.rs

@@ -0,0 +1,34 @@
+use std::char;
+
+fn main() {
+    println!("Hello, world!");
+    // ownership_ex();
+    borrowing_references();
+}
+
+
+fn ownership_transfer_ex () {
+    // this is a string literal
+    let s = "hello";
+    // this is a string
+    let ab = String::from("hello");
+    let a: char = ab.chars().nth(0).expect("REASON");
+    println!("{}", a); // outputs 'h'
+
+    // do stuff with s
+}
+// is is out of scope and therefore invalid
+
+fn borrowing_references () {
+    let mut s1 = String::from("hello");
+    change_string(&mut s1);
+    // s1 is still valid aat this point so ownership didint change
+    println!("{}", s1);
+    // do more stuff with s1
+}
+
+fn change_string (some_string: &mut String) {
+    // using borrowed value contained in some_string
+    some_string.push_str(", world");
+    // some_string out of scope and therefore invalid
+}