From f7fa0bf67ecd30779f0f10a1fbcb5e5eb37de16c Mon Sep 17 00:00:00 2001
From: Albarjas <mohamad.albarjas@siemens-healthineers.com>
Date: Thu, 21 May 2026 16:45:18 +0200
Subject: [PATCH] Implement stack functions

---
 stack.c | 43 +++++++++++++++++++++++++++++++++++--------
 stack.h | 21 +++++++++++++++------
 2 files changed, 50 insertions(+), 14 deletions(-)

diff --git a/stack.c b/stack.c
index e3a90d4..0cc348c 100644
--- a/stack.c
+++ b/stack.c
@@ -1,33 +1,60 @@
 #include <stdlib.h>
 #include "stack.h"
 
-//TODO: grundlegende Stackfunktionen implementieren:
-/*  * `push`: legt ein Element oben auf den Stack,
-    * `pop`: entfernt das oberste Element,
-    * `top`: liefert das oberste Element zurück,
-    * `clearStack`: gibt den gesamten Speicher frei. */
-
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data)
 {
+    StackNode *newNode = (StackNode *)malloc(sizeof(StackNode));
 
+    if (newNode == NULL)
+    {
+        return stack;
+    }
+
+    newNode->data = data;
+    newNode->next = stack;
+
+    return newNode;
 }
 
-// Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
-// freed by caller.)
+// 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)
 {
+    StackNode *nextNode = NULL;
 
+    if (stack != NULL)
+    {
+        nextNode = stack->next;
+        free(stack);
+    }
+
+    return nextNode;
 }
 
 // Returns the data of the top element.
 void *top(StackNode *stack)
 {
+    void *data = NULL;
 
+    if (stack != NULL)
+    {
+        data = stack->data;
+    }
+
+    return data;
 }
 
 // Clears stack and releases all memory.
 void clearStack(StackNode *stack)
 {
+    StackNode *currentNode = stack;
+    StackNode *nextNode = NULL;
 
+    while (currentNode != NULL)
+    {
+        nextNode = currentNode->next;
+        free(currentNode);
+        currentNode = nextNode;
+    }
 }
\ No newline at end of file
diff --git a/stack.h b/stack.h
index f7d542d..5e8826d 100644
--- a/stack.h
+++ b/stack.h
@@ -1,19 +1,28 @@
 #ifndef STACK_H
 #define STACK_H
 
-/* A stack is a special type of queue which uses the LIFO (last in, first out) principle. 
-This means that with each new element all other elements are pushed deeper into the stack. 
+/* A stack is a special type of queue which uses the LIFO (last in, first out) principle.
+This means that with each new element all other elements are pushed deeper into the stack.
 The latest element is taken from the stack. */
 
 #include <stdlib.h>
 
-//TODO: passenden Datentyp als struct anlegen
+/*
+ * One node of the stack.
+ * data stores a generic pointer.
+ * next points to the next element below this one.
+ */
+typedef struct StackNode
+{
+    void *data;
+    struct StackNode *next;
+} StackNode;
 
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data);
 
-// Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
-// freed by caller.)
+// 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);
 
 // Returns the data of the top element.
@@ -22,4 +31,4 @@ void *top(StackNode *stack);
 // Clears stack and releases all memory.
 void clearStack(StackNode *stack);
 
-#endif
+#endif
\ No newline at end of file