match result.

src/main.rs

@@ -15,8 +15,13 @@ fn main() {
         io::stdin().read_line(&mut guess_number)
             .expect("Failed to read line.");
 
-        let guess_number: u32 = guess_number.trim().parse()
-            .expect("Not a number.");
+        let guess_number: u32 = match guess_number.trim().parse() {
+            Ok(num) => num,
+            Err(_) => {
+                println!("Not a number.");
+                continue;
+            }
+        };
 
         println!("You guess : {:?}", guess_number);