diff --git a/18.MediatorPattern/2.Code/main.cpp b/18.MediatorPattern/2.Code/main.cpp
index 53e7a8c..0ec1743 100644
--- a/18.MediatorPattern/2.Code/main.cpp
+++ b/18.MediatorPattern/2.Code/main.cpp
@@ -41,6 +41,12 @@ int main()
 	delete fangdong3;
 	delete jungle;
 	delete jianmengtu;
+	mediator   = nullptr;
+	fangdong1  = nullptr;
+	fangdong2  = nullptr;
+	fangdong3  = nullptr;
+	jungle     = nullptr;
+	jianmengtu = nullptr;
 
 	return 0;
 }
\ No newline at end of file
diff --git a/19.MementoPattern/2.Code/main.cpp b/19.MementoPattern/2.Code/main.cpp
index bd26773..5e1a785 100644
--- a/19.MementoPattern/2.Code/main.cpp
+++ b/19.MementoPattern/2.Code/main.cpp
@@ -43,6 +43,8 @@ int main()
 
 	delete Jungle;
 	delete codeVer;
+	Jungle = nullptr;
+	codeVer = nullptr;
 
 	return 0;
 }
\ No newline at end of file
diff --git a/20.ObserverPattern/2.Code/main.cpp b/20.ObserverPattern/2.Code/main.cpp
index 1a99ff5..6c15f70 100644
--- a/20.ObserverPattern/2.Code/main.cpp
+++ b/20.ObserverPattern/2.Code/main.cpp
@@ -34,6 +34,11 @@ int main()
 	delete Single;
 	delete Jianmengtu;
 	delete SillyDog;
+	controller = nullptr;
+	Jungle     = nullptr;
+	Single     = nullptr;
+	Jianmengtu = nullptr;
+	SillyDog   = nullptr;
 
 	return 0;
 }
\ No newline at end of file
diff --git a/21.StatePattern/2.Code/main.cpp b/21.StatePattern/2.Code/main.cpp
index cfbcfc4..fd69714 100644
--- a/21.StatePattern/2.Code/main.cpp
+++ b/21.StatePattern/2.Code/main.cpp
@@ -14,6 +14,7 @@ int main()
 	system("pause");
 
 	delete jungle;
+	jungle = nullptr;
 	
 	return 0;
 }
\ No newline at end of file
diff --git a/22.StrategyPattern/2.Code/main.cpp b/22.StrategyPattern/2.Code/main.cpp
index e41924a..0ad78d2 100644
--- a/22.StrategyPattern/2.Code/main.cpp
+++ b/22.StrategyPattern/2.Code/main.cpp
@@ -26,6 +26,7 @@ int main()
 	system("pause");
 
 	delete ctx;
+	ctx = nullptr;
 
 	return 0;
 }
\ No newline at end of file
diff --git a/23.TemplateMethodPattern/2.Code/main.cpp b/23.TemplateMethodPattern/2.Code/main.cpp
index 9900170..54be41f 100644
--- a/23.TemplateMethodPattern/2.Code/main.cpp
+++ b/23.TemplateMethodPattern/2.Code/main.cpp
@@ -6,14 +6,17 @@ int main()
 	FingerprintModule *fp = new FingerprintModuleA();
 	fp->algorithm();
 	delete fp;
+	fp = nullptr;
 
 	fp = new FingerprintModuleB();
 	fp->algorithm();
 	delete fp;
+	fp = nullptr;
 
 	fp = new FingerprintModuleC();
 	fp->algorithm();
 	delete fp;
+	fp = nullptr;
 
 	printf("\n\n");
 	system("pause");
diff --git a/24.VisitorPattern/2.Code/main.cpp b/24.VisitorPattern/2.Code/main.cpp
index 2ef57e4..bc17e14 100644
--- a/24.VisitorPattern/2.Code/main.cpp
+++ b/24.VisitorPattern/2.Code/main.cpp
@@ -39,6 +39,13 @@ int main()
 	delete cashier;
 	delete jungle;
 	delete shoppingCart;
+	apple1 = nullptr;
+	apple2 = nullptr;
+	book1 = nullptr;
+	book2 = nullptr;
+	cashier = nullptr;
+	jungle = nullptr;
+	shoppingCart = nullptr;
 
 	return 0;
 }
\ No newline at end of file