Finished first draw of stack, next step: writing tests

stack.c

@@ -10,6 +10,18 @@
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data)
 {
+    if(!(stack)) { // check if stack is empty
+        stack = malloc(sizeof(StackNode));
+        stack->stackData = data;
+        stack->below = NULL;
+        return stack;
+    }
+
+    StackNode* newStack = malloc(sizeof(StackNode));
+    newStack->below = stack;
+    newStack->stackData = data;
+    stack = newStack;
+    return stack;
 
 }
 
@@ -17,17 +29,37 @@ StackNode *push(StackNode *stack, void *data)
 // freed by caller.)
 StackNode *pop(StackNode *stack)
 {
-
+    if(stack) {
+        StackNode* temp = stack;
+        stack = stack->below;
+        free(temp->data);
+        temp->stackData = NULL;
+        free(temp);
+        temp = NULL;
+        return stack;
+    } else {
+        return NULL;
+    }
 }
 
 // Returns the data of the top element.
 void *top(StackNode *stack)
 {
+    if(stack)
+        return stack->stackData;
+    else
+        return NULL;
 
 }
 
 // Clears stack and releases all memory.
 void clearStack(StackNode *stack)
 {
+    if(stack) {
+        do {
+            stack = pop(stack);
+        } while (stack->below);
+        pop(stack);
+    }
 
 }

stack.h

@@ -9,6 +9,11 @@ The latest element is taken from the stack. */
 
 //TODO: passenden Datentyp als struct anlegen
 
+typedef struct StackNode {
+    StackNode* below;
+    void* stackData;
+} StackNode;
+
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data);