diff --git a/stack.c b/stack.c
index e3a90d4..ea5d804 100644
--- a/stack.c
+++ b/stack.c
@@ -10,24 +10,54 @@
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data)
 {
+    // Neues Stack-Element erstellen
+    StackNode *newNode = malloc(sizeof(StackNode));
+    if (!newNode) {
+        return stack; // oder NULL, je nach Fehlerstrategie
+    }
 
+    
+    newNode->data = data;
+    newNode->next = stack; // bisheriger Stack wird nach unten geschoben
+
+    return newNode; // neuer Kopf des Stacks
 }
 
 // Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
 // freed by caller.)
 StackNode *pop(StackNode *stack)
 {
+   if (stack == NULL)
+        return NULL;
 
+    StackNode *newTop = stack->next;
+
+    // Daten gehen verloren!
+    // Caller KANN sie nicht freigeben.
+    free(stack);
+
+    return newTop;
 }
 
 // Returns the data of the top element.
 void *top(StackNode *stack)
 {
+    if (stack == NULL)
+        return NULL;   // kein Element im Stack
 
+    return stack->data;
 }
 
 // Clears stack and releases all memory.
 void clearStack(StackNode *stack)
 {
+    StackNode *current = stack;
+
+    while (current != NULL) 
+    {
+        StackNode *next = current->next;
+        free(current);
+        current = next;
+    }
 
 }
\ No newline at end of file
diff --git a/stack.h b/stack.h
index f7d542d..2506346 100644
--- a/stack.h
+++ b/stack.h
@@ -8,6 +8,10 @@ The latest element is taken from the stack. */
 #include <stdlib.h>
 
 //TODO: passenden Datentyp als struct anlegen
+typedef struct Node {
+    void *data;
+    struct Node *next;
+} StackNode;
 
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data);