stack.c

@@ -20,33 +20,33 @@
 
 StackNode *createNode(void *data) {
 
-  StackNode *node = malloc(sizeof(StackNode));
+  StackNode *node =
+      malloc(sizeof(StackNode)); // Speicher reservieren, Speicherplatz für das
+                                 // struct StackNode
 
   if (node == NULL)
-    return NULL;
+    return NULL; // Speicher konnte nicht reserviert werden
 
-  node->data = data;
-  node->next = NULL;
-  node->prev = NULL;
+  node->data = data; // Zeiger auf data neuer node
+  node->next = NULL; // nächster Zeiger ist NULL, Ende der Liste
 
-  return node;
+  return node; // pointer auf den neuen Knoten zurückgeben
 }
 
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data) {
 
-  StackNode *newNode = createNode(data);
+  StackNode *newNode = createNode(data); // Speicher für neuen Knoten
+                                         // reservieren
 
-  if (newNode == NULL) {
+  if (newNode == NULL) { // wenn Speicher nicht reserviert werden konnte, wird
+                         // stack unverändert zurückgegeben
     return stack;
   }
 
-  newNode->next = stack;
-  if (stack != NULL) {
-    stack->prev = newNode;
-  }
+  newNode->next = stack; // pointer verschieben
 
-  return newNode;
+  return newNode; // Zeiger auf neuen Speicherbereich zurückgeben
 }
 
 // Deletes the top element of the stack (latest added element) and releases its
@@ -57,9 +57,6 @@ StackNode *pop(StackNode *stack) {
     return NULL;
 
   StackNode *nextNode = stack->next;
-  if (nextNode != NULL) {
-    nextNode->prev = NULL;
-  }
 
   free(stack);
 
@@ -69,14 +66,17 @@ StackNode *pop(StackNode *stack) {
 }
 
 // Returns the data of the top element.
-void *top(StackNode *stack) { return stack ? stack->data : NULL; }
+void *top(StackNode *stack) { return stack != NULL ? stack->data : NULL; }
 
 // Clears stack and releases all memory.
-void clearStack(StackNode **stack) {
+StackNode *clearStack(StackNode *stack) {
 
-  while (*stack != NULL) {
-    StackNode *next = (*stack)->next;
-    free(*stack);
-    *stack = next;
+  while (stack != NULL) {
+
+    StackNode *next = stack->next;
+    free(stack);
+    stack = next;
   }
+
+  return NULL;
 }

stack.h

@@ -13,7 +13,6 @@ typedef struct StackNode {
 
   void *data;
   struct StackNode *next;
-  struct StackNode *prev;
 
 } StackNode;
 
@@ -30,6 +29,6 @@ StackNode *pop(StackNode *stack);
 void *top(StackNode *stack);
 
 // Clears stack and releases all memory.
-void clearStack(StackNode **stack);
+StackNode *clearStack(StackNode *stack);
 
 #endif

test_stack.c

@@ -8,12 +8,14 @@
 void test_createNode(void) {
 
   int testInt = 26;
+
   StackNode *testNode = createNode(&testInt);
 
   TEST_ASSERT_NOT_NULL(testNode);
+
   TEST_ASSERT_EQUAL_PTR(&testInt, testNode->data);
+
   TEST_ASSERT_NULL(testNode->next);
-  TEST_ASSERT_NULL(testNode->prev);
 
   free(testNode);
 }
@@ -25,16 +27,17 @@ void test_deleteTopElement(void) {}
 void test_returnData(void) {}
 
 void test_clearStack(void) {
+
   int testInts[] = {1, 2, 3, 4, 5};
-  StackNode *stack = NULL;
+  StackNode *testStack = NULL;
 
   for (int i = 0; i < 5; i++) {
-    stack = push(stack, &testInts[i]);
+
+    testStack = push(testStack, &testInts[i]);
   }
 
-  clearStack(&stack);
-
-  TEST_ASSERT_NULL(stack);
+  testStack = clearStack(testStack);
+  TEST_ASSERT_NULL(testStack);
 }
 
 void setUp(void) {}
@@ -45,7 +48,6 @@ int main(void) {
   UNITY_BEGIN();
 
   printf("------------------------stack test------------------------\n");
-
   RUN_TEST(test_createNode);
   RUN_TEST(test_pushDataToStack);
   RUN_TEST(test_deleteTopElement);