function clearStack is done

stack.c

@@ -41,5 +41,12 @@ 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;
+  }
 }