resolved 'previous definition' in 'classes'

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";
 }

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
 {

classes/main.cpp

@@ -1,4 +1,3 @@
-#include "tier.cpp"
 #include "hund.cpp"
 #include "katze.cpp"
 #include <stdio.h>

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;
-}
+}
+#endif

classes/tier.h

@@ -0,0 +1,11 @@
+#include<stdio.h>
+#include <string>
+
+class tier{
+    public:
+        tier();
+
+        std::string getLaut();
+    protected:
+        std::string Laut;
+};