Merge pull request '修改' (#2) from develop into main

src/MathExamGenerator.java

@@ -62,6 +62,7 @@ public class MathExamGenerator {
         String input = reader.readLine();
 
         if (input == null || input.trim().isEmpty()) {
+            System.out.println("输入不能为空，请重新输入");
             return;
         } else if (input.equals("exit")) {
             isRunning = false;
@@ -191,7 +192,8 @@ public class MathExamGenerator {
                     isRunning = false;
                     break;
                 default:
-                    // 继续生成题目，不需要额外操作
+                    System.out.println("无效的选项，请重新输入");
+                    handleUserChoice();
                     break;
             }
         } catch (IOException e) {