diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index 6eb2a49..ea8c818 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -9,10 +9,9 @@
     <option name="autoReloadType" value="SELECTIVE" />
   </component>
   <component name="ChangeListManager">
-    <list default="true" id="1201acd7-f240-4a23-9c12-26bf9afcb8cb" name="更改" comment="合并更改">
-      <change afterPath="$PROJECT_DIR$/.idea/artifacts/TestSystem_jar.xml" afterDir="false" />
+    <list default="true" id="1201acd7-f240-4a23-9c12-26bf9afcb8cb" name="更改" comment="修复除零bug">
       <change beforePath="$PROJECT_DIR$/.idea/workspace.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/workspace.xml" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/main/java/com/mathapp/services/DataPersistence.java" beforeDir="false" afterPath="$PROJECT_DIR$/src/main/java/com/mathapp/services/DataPersistence.java" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/target/classes/com/mathapp/problemGenerators/HighSchoolProblemGenerator.class" beforeDir="false" afterPath="$PROJECT_DIR$/target/classes/com/mathapp/problemGenerators/HighSchoolProblemGenerator.class" afterDir="false" />
     </list>
     <option name="SHOW_DIALOG" value="false" />
     <option name="HIGHLIGHT_CONFLICTS" value="true" />
@@ -47,10 +46,10 @@
     </option>
     <option name="RECENT_GIT_ROOT_PATH" value="$PROJECT_DIR$" />
   </component>
-  <component name="KubernetesApiPersistence"><![CDATA[{}]]></component>
-  <component name="KubernetesApiProvider"><![CDATA[{
-  "isMigrated": true
-}]]></component>
+  <component name="KubernetesApiPersistence">{}</component>
+  <component name="KubernetesApiProvider">{
+  &quot;isMigrated&quot;: true
+}</component>
   <component name="ProjectColorInfo">{
   &quot;customColor&quot;: &quot;&quot;,
   &quot;associatedIndex&quot;: 1
@@ -61,25 +60,25 @@
     <option name="hideEmptyMiddlePackages" value="true" />
     <option name="showLibraryContents" value="true" />
   </component>
-  <component name="PropertiesComponent"><![CDATA[{
-  "keyToString": {
-    "RunOnceActivity.ShowReadmeOnStart": "true",
-    "SHARE_PROJECT_CONFIGURATION_FILES": "true",
-    "git-widget-placeholder": "liwentao__branch",
-    "kotlin-language-version-configured": "true",
-    "node.js.detected.package.eslint": "true",
-    "node.js.detected.package.tslint": "true",
-    "node.js.selected.package.eslint": "(autodetect)",
-    "node.js.selected.package.tslint": "(autodetect)",
-    "nodejs_package_manager_path": "npm",
-    "onboarding.tips.debug.path": "C:/Users/Teptao/Desktop/软件工程导论/结对项目/TestSystem/src/main/java/org/example/Main.java",
-    "project.structure.last.edited": "工件",
-    "project.structure.proportion": "0.15",
-    "project.structure.side.proportion": "0.2",
-    "vue.rearranger.settings.migration": "true",
-    "应用程序.MathApp.executor": "Run"
+  <component name="PropertiesComponent">{
+  &quot;keyToString&quot;: {
+    &quot;RunOnceActivity.ShowReadmeOnStart&quot;: &quot;true&quot;,
+    &quot;SHARE_PROJECT_CONFIGURATION_FILES&quot;: &quot;true&quot;,
+    &quot;git-widget-placeholder&quot;: &quot;liwentao__branch&quot;,
+    &quot;kotlin-language-version-configured&quot;: &quot;true&quot;,
+    &quot;node.js.detected.package.eslint&quot;: &quot;true&quot;,
+    &quot;node.js.detected.package.tslint&quot;: &quot;true&quot;,
+    &quot;node.js.selected.package.eslint&quot;: &quot;(autodetect)&quot;,
+    &quot;node.js.selected.package.tslint&quot;: &quot;(autodetect)&quot;,
+    &quot;nodejs_package_manager_path&quot;: &quot;npm&quot;,
+    &quot;onboarding.tips.debug.path&quot;: &quot;C:/Users/Teptao/Desktop/软件工程导论/结对项目/TestSystem/src/main/java/org/example/Main.java&quot;,
+    &quot;project.structure.last.edited&quot;: &quot;工件&quot;,
+    &quot;project.structure.proportion&quot;: &quot;0.15&quot;,
+    &quot;project.structure.side.proportion&quot;: &quot;0.2&quot;,
+    &quot;vue.rearranger.settings.migration&quot;: &quot;true&quot;,
+    &quot;应用程序.MathApp.executor&quot;: &quot;Run&quot;
   }
-}]]></component>
+}</component>
   <component name="RunManager">
     <configuration name="MathApp" type="Application" factoryName="Application" temporary="true" nameIsGenerated="true">
       <option name="MAIN_CLASS_NAME" value="com.mathapp.MathApp" />
@@ -99,6 +98,7 @@
         <item itemvalue="应用程序.MathApp" />
         <item itemvalue="应用程序.MathApp" />
         <item itemvalue="应用程序.MathApp" />
+        <item itemvalue="应用程序.MathApp" />
       </list>
     </recent_temporary>
   </component>
@@ -160,7 +160,23 @@
       <option name="project" value="LOCAL" />
       <updated>1760136867337</updated>
     </task>
-    <option name="localTasksCounter" value="6" />
+    <task id="LOCAL-00006" summary="修复使用用户名登录时无法修改密码的问题">
+      <option name="closed" value="true" />
+      <created>1760182983400</created>
+      <option name="number" value="00006" />
+      <option name="presentableId" value="LOCAL-00006" />
+      <option name="project" value="LOCAL" />
+      <updated>1760182983400</updated>
+    </task>
+    <task id="LOCAL-00007" summary="修复除零bug">
+      <option name="closed" value="true" />
+      <created>1760183246928</created>
+      <option name="number" value="00007" />
+      <option name="presentableId" value="LOCAL-00007" />
+      <option name="project" value="LOCAL" />
+      <updated>1760183246928</updated>
+    </task>
+    <option name="localTasksCounter" value="8" />
     <servers />
   </component>
   <component name="TypeScriptGeneratedFilesManager">
@@ -193,6 +209,8 @@
     <MESSAGE value="创建maven项目" />
     <MESSAGE value="初步框架" />
     <MESSAGE value="合并更改" />
-    <option name="LAST_COMMIT_MESSAGE" value="合并更改" />
+    <MESSAGE value="修复使用用户名登录时无法修改密码的问题" />
+    <MESSAGE value="修复除零bug" />
+    <option name="LAST_COMMIT_MESSAGE" value="修复除零bug" />
   </component>
 </project>
\ No newline at end of file
diff --git a/src/main/java/com/mathapp/panels/MainMenuPanel.java b/src/main/java/com/mathapp/panels/MainMenuPanel.java
index 3afece3..68ffc43 100644
--- a/src/main/java/com/mathapp/panels/MainMenuPanel.java
+++ b/src/main/java/com/mathapp/panels/MainMenuPanel.java
@@ -86,6 +86,15 @@ public class MainMenuPanel extends JPanel {
   }
 
   private void handleStart() {
+
+    ButtonModel selectedModel = levelGroup.getSelection();
+
+    // 关键检查：判断是否有按钮被选中
+    if (selectedModel == null) {
+      JOptionPane.showMessageDialog(this, "请先选择一个难度级别！", "选择错误", JOptionPane.WARNING_MESSAGE);
+      return; // 发现未选择后，直接退出方法，不执行后续逻辑
+    }
+
     String level = levelGroup.getSelection().getActionCommand();
     int count;
     try {
diff --git a/target/classes/com/mathapp/panels/MainMenuPanel.class b/target/classes/com/mathapp/panels/MainMenuPanel.class
index a7ada08..2992fe9 100644
Binary files a/target/classes/com/mathapp/panels/MainMenuPanel.class and b/target/classes/com/mathapp/panels/MainMenuPanel.class differ
diff --git a/target/classes/com/mathapp/problemGenerators/HighSchoolProblemGenerator.class b/target/classes/com/mathapp/problemGenerators/HighSchoolProblemGenerator.class
index e982df6..a8f572c 100644
Binary files a/target/classes/com/mathapp/problemGenerators/HighSchoolProblemGenerator.class and b/target/classes/com/mathapp/problemGenerators/HighSchoolProblemGenerator.class differ