diff --git a/classes/hund.cpp b/classes/hund.cpp
index bc99488..69e6e27 100644
--- a/classes/hund.cpp
+++ b/classes/hund.cpp
@@ -1,12 +1,14 @@
-// #include "tier.cpp"
+#ifndef TIER_H // ensuring that this object is only initialized once
+#include "tier.cpp"
+#endif
 
 class hund : public tier
 {
-    public:
-        hund();
+public:
+    hund();
 };
 
 hund::hund() : tier()
 {
-    Laut =  "wuff";
+    Laut = "wuff";
 }
\ No newline at end of file
diff --git a/classes/katze.cpp b/classes/katze.cpp
index 4959af9..c2d72c7 100644
--- a/classes/katze.cpp
+++ b/classes/katze.cpp
@@ -1,4 +1,6 @@
-// #include "tier.cpp"
+#ifndef TIER_H //ensuring that this object is only initialized once
+#include "tier.cpp"
+#endif
 
 class katze : public tier
 {
diff --git a/classes/main.cpp b/classes/main.cpp
index 4adc7ec..ee5e36f 100644
--- a/classes/main.cpp
+++ b/classes/main.cpp
@@ -1,4 +1,3 @@
-#include "tier.cpp"
 #include "hund.cpp"
 #include "katze.cpp"
 #include <stdio.h>
diff --git a/classes/program b/classes/program
index fbb60f2..056b0ff 100755
Binary files a/classes/program and b/classes/program differ
diff --git a/classes/tier.cpp b/classes/tier.cpp
index 66b0190..eb37fd3 100644
--- a/classes/tier.cpp
+++ b/classes/tier.cpp
@@ -1,22 +1,28 @@
-#include<stdio.h>
+#ifndef TIER_H
+#define TIER_H
+#include <stdio.h>
 #include <string>
+#include "tier.h"
 
-class tier{
-    public:
-        tier();
+// class tier
+// {
+// public:
+//     tier();
 
-        std::string getLaut();
-    protected:
-        std::string Laut;
-};
+//     std::string getLaut();
 
-tier::tier() {
-this->Laut = "void";
+// protected:
+//     std::string Laut;
+// };
 
-}    
+tier::tier()
+{
+    this->Laut = "void";
+}
 
 std::string tier::getLaut()
 {
 
     return this->Laut;
-}
\ No newline at end of file
+}
+#endif
\ No newline at end of file
diff --git a/classes/tier.h b/classes/tier.h
new file mode 100644
index 0000000..3671f22
--- /dev/null
+++ b/classes/tier.h
@@ -0,0 +1,11 @@
+#include<stdio.h>
+#include <string>
+
+class tier{
+    public:
+        tier();
+
+        std::string getLaut();
+    protected:
+        std::string Laut;
+};