diff --git a/day7/homework/h7.cpp b/day7/homework/h7.cpp
index eb0c8db..dbc7916 100644
--- a/day7/homework/h7.cpp
+++ b/day7/homework/h7.cpp
@@ -44,6 +44,7 @@ catch (int e)
 ********************************************************************/
 
 #include <iostream>
+#include <typeinfo>
 
 using namespace std;
 
@@ -74,51 +75,60 @@ public:
 int main()
 {
     Animal *ap = new Animal(); // 创建一个 Animal 类型的指针
+
     try
     {
         Cat *cp = dynamic_cast<Cat *>(ap); // 将其转换为 Cat 类型的指针
-        cp->meow();
+        if (cp)
+            cp->meow();
+        else
+            throw 1;
     }
-    catch (int e)
+    catch (int &e)
     {
-        cout << "dynamic_cast 将 Animal 转换为 Cat 失败" << endl
-             << e << endl;
+        cout << "dynamic_cast 将 Animal 转换为 Cat 失败" << endl;
     }
 
     Animal *ap2 = new Animal(); // 创建一个 Animal 类型的指针
     try
     {
         Dog *dp = dynamic_cast<Dog *>(ap2); // 将其转换为 Dog 类型的指针
-        dp->bark();
+        if (dp)
+            dp->bark();
+        else
+            throw 1;
     }
-    catch (int e)
+    catch (int &e)
     {
-        cout << "dynamic_cast 将 Animal 转换为 Dog 失败" << endl
-             << e << endl;
+        cout << "dynamic_cast 将 Animal 转换为 Dog 失败" << endl;
     }
 
     Cat *cp2 = new Cat(); // 创建一个 Cat 类型的指针
     try
     {
         Animal *ap3 = dynamic_cast<Animal *>(cp2); // 将其转换为 Animal 类型的指针
-        cout << "dynamic_cast 将 Cat 转换为 Animal 成功" << endl;
+        if (ap3)
+            cout << "dynamic_cast 将 Cat 转换为 Animal 成功" << endl;
+        else
+            throw 1;
     }
-    catch (int e)
+    catch (int &e)
     {
-        cout << "dynamic_cast 将 Cat 转换为 Animal 失败" << endl
-             << e << endl;
+        cout << "dynamic_cast 将 Cat 转换为 Animal 失败" << endl;
     }
 
     Dog *dp2 = new Dog(); // 创建一个 Dog 类型的指针
     try
     {
         Animal *ap4 = dynamic_cast<Animal *>(dp2); // 将其转换为 Animal 类型的指针
-        cout << "dynamic_cast 将 Dog 转换为 Animal 成功" << endl;
+        if (ap4)
+            cout << "dynamic_cast 将 Dog 转换为 Animal 成功" << endl;
+        else
+            throw 1;
     }
-    catch (int e)
+    catch (int &e)
     {
-        cout << "dynamic_cast 将 Dog 转换为 Animal 失败" << endl
-             << e << endl;
+        cout << "dynamic_cast 将 Dog 转换为 Animal 失败" << endl;
     }
 
     return 0;