diff --git a/06-Preemptive/os.c b/06-Preemptive/os.c
index b5e4cc8..04b63dc 100644
--- a/06-Preemptive/os.c
+++ b/06-Preemptive/os.c
@@ -17,8 +17,8 @@
 
 void usart_init(void)
 {
-	*(RCC_APB2ENR) |= (uint32_t) (0x00000001 | 0x00000004);
-	*(RCC_APB1ENR) |= (uint32_t) (0x00020000);
+	*(RCC_APB2ENR) |= (uint32_t)(0x00000001 | 0x00000004);
+	*(RCC_APB1ENR) |= (uint32_t)(0x00020000);
 
 	/* USART2 Configuration, Rx->PA3, Tx->PA2 */
 	*(GPIOA_CRL) = 0x00004B00;
@@ -48,6 +48,11 @@ void delay(int count)
 	while (count--);
 }
 
+struct task_c_b {
+	unsigned int stack[STACK_SIZE];
+	unsigned int * usertask;
+} typedef tcb;
+
 /* Exception return behavior */
 #define HANDLER_MSP	0xFFFFFFF1
 #define THREAD_MSP	0xFFFFFFF9
@@ -105,19 +110,19 @@ void task2_func(void)
 
 int main(void)
 {
-	unsigned int user_stacks[TASK_LIMIT][STACK_SIZE];
-	unsigned int *usertasks[TASK_LIMIT];
+	tcb user_proc[TASK_LIMIT];
 	size_t task_count = 0;
 	size_t current_task;
+	size_t next_task;
 
 	usart_init();
 
 	print_str("OS: Starting...\n");
 	print_str("OS: First create task 1\n");
-	usertasks[0] = create_task(user_stacks[0], &task1_func);
+	user_proc[0].usertask = create_task(user_proc[0].stack, &task1_func);
 	task_count += 1;
 	print_str("OS: Back to OS, create task 2\n");
-	usertasks[1] = create_task(user_stacks[1], &task2_func);
+	user_proc[1].usertask = create_task(user_proc[1].stack, &task2_func);
 	task_count += 1;
 
 	print_str("\nOS: Start round-robin scheduler!\n");
@@ -127,13 +132,15 @@ int main(void)
 	*SYSTICK_VAL = 0;
 	*SYSTICK_CTRL = 0x07;
 	current_task = 0;
+	next_task = current_task == (task_count - 1) ? 0 : current_task + 1;
 
 	while (1) {
 		print_str("OS: Activate next task\n");
-		usertasks[current_task] = activate(usertasks[current_task]);
+		user_proc[current_task].usertask = activate(user_proc[current_task].usertask);
 		print_str("OS: Back to OS\n");
 
-		current_task = current_task == (task_count - 1) ? 0 : current_task + 1;
+		current_task = next_task;
+		next_task = current_task == (task_count - 1) ? 0 : current_task + 1;
 	}
 
 	return 0;