update old book references to the second edition of the book

primitive_types/primitive_types3.rs

@@ -39,8 +39,9 @@ fn main() {
 
 
 // There's a shorthand to initialize Arrays with a certain size that does not 
-// require you to type in 100 items (but you certainly can if you want!)
-// Check out the Primitive Types -> Arrays section of the book:
-// https://doc.rust-lang.org/stable/book/second-edition/ch03-02-data-types.html#arrays
+// require you to type in 100 items (but you certainly can if you want!).
+// For example, you can do:
+// let array = ["Are we there yet?"; 10];
+
 // Bonus: what are some other things you could have that would return true
 // for `a.len() >= 100`?

primitive_types/primitive_types4.rs

@@ -38,12 +38,12 @@ fn main() {
 
 
 
-// Take a look at the Primitive Types -> Slices section of the book:
-// http://doc.rust-lang.org/stable/book/primitive-types.html#slices
+// Take a look at the Understanding Ownership -> Slices -> Other Slices section of the book:
+// https://doc.rust-lang.org/stable/book/second-edition/ch04-03-slices.html#other-slices
 // and use the starting and ending indices of the items in the Array
 // that you want to end up in the slice.
 
 // If you're curious why the right hand of the `==` comparison does not
 // have an ampersand for a reference since the left hand side is a
-// reference, take a look at the Deref coercions chapter:
-// http://doc.rust-lang.org/stable/book/deref-coercions.html
+// reference, take a look at the Deref coercions section of the book:
+// https://doc.rust-lang.org/stable/book/second-edition/ch15-02-deref.html#implicit-deref-coercions-with-functions-and-methods

primitive_types/primitive_types5.rs

@@ -38,8 +38,8 @@ fn main() {
 
 
 
-// Take a look at the Primitive Types -> Tuples section of the book:
-// http://doc.rust-lang.org/stable/book/primitive-types.html#tuples
-// Particularly the part about "destructuring lets". You'll need to
-// make a pattern to bind `name` and `age` to the appropriate parts
+// Take a look at the Data Types -> The Tuple Type section of the book:
+// https://doc.rust-lang.org/stable/book/second-edition/ch03-02-data-types.html#the-tuple-type
+// Particularly the part about destructuring (second to last example in the section). 
+// You'll need to make a pattern to bind `name` and `age` to the appropriate parts
 // of the tuple. You can do it!!

primitive_types/primitive_types6.rs

@@ -39,6 +39,7 @@ fn main() {
 
 
 // While you could use a destructuring `let` for the tuple here, try 
-// indexing into it instead, as explained here:
-// http://doc.rust-lang.org/stable/book/primitive-types.html#tuple-indexing
+// indexing into it instead, as explained in the last example of the 
+// Data Types -> The Tuple Type section of the book:
+// https://doc.rust-lang.org/stable/book/second-edition/ch03-02-data-types.html#the-tuple-type
 // Now you have another tool in your toolbox!