add one more example

src/bin/example3.rs

@@ -0,0 +1,85 @@
+// https://doc.rust-lang.org/rust-by-example/variable_bindings.html
+fn example3a() {
+    let an_integer = 1u32;
+    let a_boolean = true;
+    let unit = ();
+
+    // copy `an_integer` into `copied_integer`
+    let copied_integer = an_integer;
+
+    println!("An integer: {:?}", copied_integer);
+    println!("A boolean: {:?}", a_boolean);
+    println!("Meet the unit value: {:?}", unit);
+
+    // The compiler warns about unused variable bindings; these warnings can
+    // be silenced by prefixing the variable name with an underscore
+    let _unused_variable = 3u32;
+
+    let noisy_unused_variable = 2u32;
+    // FIXME ^ Prefix with an underscore to suppress the warning
+    // Please note that warnings may not be shown in a browser
+}
+
+// https://doc.rust-lang.org/rust-by-example/variable_bindings/mut.html
+fn example3b() {
+    let _immutable_binding = 1;
+    let mut mutable_binding = 1;
+
+    println!("Before mutation: {}", mutable_binding);
+
+    // Ok
+    mutable_binding += 1;
+
+    println!("After mutation: {}", mutable_binding);
+
+    // Error!
+    // _immutable_binding += 1;
+    // FIXME ^ Comment out this line
+}
+
+// https://doc.rust-lang.org/rust-by-example/variable_bindings/scope.html
+fn example3c() {
+    // This binding lives in the main function
+    let long_lived_binding = 1;
+
+    // This is a block, and has a smaller scope than the main function
+    {
+        // This binding only exists in this block
+        let short_lived_binding = 2;
+
+        println!("inner short: {}", short_lived_binding);
+    }
+    // End of the block
+
+    // Error! `short_lived_binding` doesn't exist in this scope
+    // println!("outer short: {}", short_lived_binding);
+    // FIXME ^ Comment out this line
+
+    println!("outer long: {}", long_lived_binding);
+}
+
+// https://doc.rust-lang.org/rust-by-example/variable_bindings/freeze.html
+fn example3d() {
+    let mut _mutable_integer = 7i32;
+
+    {
+        // Shadowing by immutable `_mutable_integer`
+        let _mutable_integer = _mutable_integer;
+
+        // Error! `_mutable_integer` is frozen in this scope
+        // _mutable_integer = 50;
+        // FIXME ^ Comment out this line
+
+        // `_mutable_integer` goes out of scope
+    }
+
+    // Ok! `_mutable_integer` is not frozen in this scope
+    _mutable_integer = 3;
+}
+
+pub fn main() {
+    example3a();
+    example3b();
+    example3c();
+    example3d();
+}

src/bin/hello_world.rs

@@ -1,3 +1,15 @@
+// This is a comment, and is ignored by the compiler
+// You can test this code by clicking the "Run" button over there ->
+// or if you prefer to use your keyboard, you can use the "Ctrl + Enter" shortcut
+
+// This code is editable, feel free to hack it!
+// You can always return to the original code by clicking the "Reset" button ->
+
+// This is the main function
 fn main() {
+    // Statements here are executed when the compiled binary is called
+
+    // Print text to the console
     println!("Hello World! This is an APE built with Rust.");
 }
+