Update Main.java

src/Main.java

@@ -3,6 +3,8 @@ public class Main {
     ExamSystem system = new ExamSystem();
     while (true) {
       Users users = system.login();
+      System.out.print("准备生成" + users.getType()
+          + "数学题目，请输入生成题目数量（输入-1将退出当前用户，重新登录）：");
       system.generateProblems(users);
     }
   }