Address loop labels and continue. Fixes #1392.

listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "loops"
+version = "0.1.0"
+edition = "2018"
+
+[dependencies]

listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/output.txt

@@ -0,0 +1,12 @@
+   Compiling loops v0.1.0 (file:///projects/loops)
+    Finished dev [unoptimized + debuginfo] target(s) in 0.58s
+     Running `target/debug/loops`
+count = 0
+remaining = 10
+remaining = 9
+count = 1
+remaining = 10
+remaining = 9
+count = 2
+remaining = 10
+End count = 2

listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/src/main.rs

@@ -0,0 +1,21 @@
+fn main() {
+    let mut count = 0;
+    'counting_up: loop {
+        println!("count = {}", count);
+        let mut remaining = 10;
+
+        loop {
+            println!("remaining = {}", remaining);
+            if remaining == 9 {
+                break;
+            }
+            if count == 2 {
+                break 'counting_up;
+            }
+            remaining -= 1;
+        }
+
+        count += 1;
+    }
+    println!("End count = {}", count);
+}

src/ch03-05-control-flow.md

@@ -220,13 +220,36 @@ The symbol `^C` represents where you pressed <span class="keystroke">ctrl-c
 depending on where the code was in the loop when it received the interrupt
 signal.
 
-Fortunately, Rust provides another, more reliable way to break out of a loop.
-You can place the `break` keyword within the loop to tell the program when to
-stop executing the loop. Recall that we did this in the guessing game in the
+Fortunately, Rust provides a way to break out of a loop from code. You can
+place the `break` keyword within the loop to tell the program when to stop
+executing the loop. Recall that we did this in the guessing game in the
 [“Quitting After a Correct Guess”][quitting-after-a-correct-guess]<!-- ignore
 --> section of Chapter 2 to exit the program when the user won the game by
 guessing the correct number.
 
+We also used `continue` in the guessing game. The `continue` keyword within a
+loop tells the program to skip over any remaining code in this iteration of the
+loop and go to the next iteration.
+
+If you have loops within loops, `break` and `continue` apply to the innermost
+loop at that point. You can optionally specify a *loop label* on a loop and
+then use the label with `break` or `continue` to have those keywords applied to
+the labeled loop instead of the innermost loop. Here's an example with two
+nested loops:
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/src/main.rs}}
+```
+
+The outer loop has the label `'counting_up`, and it will count up from 0 to 2.
+The inner loop without a label counts down from 10 to 9. The first `break` that
+doesn't specify a label will exit the inner loop only. The `break
+'counting_up;` statement will exit the outer loop. This code prints:
+
+```console
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/output.txt}}
+```
+
 #### Returning Values from Loops
 
 One of the uses of a `loop` is to retry an operation you know might fail, such