implement stack with some initial testing

makefile

@@ -35,8 +35,11 @@ $(program_obj_filesobj_files): %.o: %.c
 # --------------------------
 # Unit Tests
 # --------------------------
-unitTests:
-	echo "needs to be implemented"
+TEST_STACK_SOURCES = stack.c test_stack.c $(unityfolder)/unity.c
+
+stackTests: $(TEST_STACK_SOURCES) stack.h
+	$(CC) $(FLAGS) -I$(unityfolder) $(TEST_STACK_SOURCES) -o runStackTests
+	./runStackTests
 
 # --------------------------
 # Clean

stack.c

@@ -1,33 +1,55 @@
 #include <stdlib.h>
 #include "stack.h"
 
-//TODO: grundlegende Stackfunktionen implementieren:
+// 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. */
+ * `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)
 {
+    // this is the new top node
+    StackNode *newTopNode = malloc(sizeof(StackNode));
 
+    if (newTopNode == NULL)
+    {
+        return NULL;
+    }
+
+    newTopNode->data = data;
+    newTopNode->next = stack;
+
+    return newTopNode;
 }
 
 // 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)
+    {
+        return NULL;
+    }
+    StackNode *nextNode = stack->next;
+    free(stack);
+    return nextNode;
 }
 
 // Returns the data of the top element.
 void *top(StackNode *stack)
 {
-
+    if (!stack)
+    {
+        return NULL;
+    }
+    return stack->data;
 }
 
 // Clears stack and releases all memory.
 void clearStack(StackNode *stack)
 {
-
+    while (pop(stack))
+        ;
 }

stack.h

@@ -1,13 +1,17 @@
 #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
+typedef struct StackNode
+{
+    struct StackNode *next;
+    void *data;
+} StackNode;
 
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data);

test_stack.c

@@ -0,0 +1,47 @@
+#include "unity.h"
+#include "stack.h"
+
+int data1 = 10;
+int data2 = 20;
+int data3 = 30;
+
+StackNode *stack = NULL;
+
+void setUp(void)
+{
+    // set stuff up here
+}
+
+void tearDown(void)
+{
+    clearStack(stack);
+}
+
+void test_push_and_pop(void)
+{
+    stack = push(stack, &data1);
+    stack = push(stack, &data2);
+    stack = push(stack, &data3);
+
+    TEST_ASSERT_EQUAL_PTR(top(stack), &data3);
+    stack = pop(stack);
+    TEST_ASSERT_EQUAL_PTR(top(stack), &data2);
+    stack = pop(stack);
+    TEST_ASSERT_EQUAL_PTR(top(stack), &data1);
+    stack = pop(stack);
+}
+
+void test_handle_NULL(void)
+{
+    TEST_ASSERT_NULL(pop(stack));
+    TEST_ASSERT_NULL(top(stack));
+}
+
+int main(void)
+{
+    printf("============================\nStack tests\n============================\n");
+    UNITY_BEGIN();
+    RUN_TEST(test_push_and_pop);
+    RUN_TEST(test_handle_NULL);
+    return UNITY_END();
+}