Update main.rs

fix "While let Conditional Loops" Code not match

listings/ch19-patterns-and-matching/listing-19-02/src/main.rs

@@ -1,14 +1,13 @@
 fn main() {
     // ANCHOR: here
-    let (tx, rx) = std::sync::mpsc::channel();
+    let mut stack = Vec::new();
-    std::thread::spawn(move || {
-        for val in [1, 2, 3] {
-            tx.send(val).unwrap();
-        }
-    });
 
-    while let Ok(value) = rx.recv() {
+    stack.push(1);
-        println!("{value}");
+    stack.push(2);
+    stack.push(3);
+
+    while let Some(top) = stack.pop() {
+        println!("{top}");
     }
     // ANCHOR_END: here
 }