diff --git a/week4/main.c b/week4/main.c
new file mode 100644
index 0000000..97536aa
--- /dev/null
+++ b/week4/main.c
@@ -0,0 +1,22 @@
+#include "queue.h"
+#include <stdbool.h>
+#include <stdio.h>
+
+int main(void) {
+	Queue queue;
+	double value;
+	CreateQueue(&queue, 5);
+	puts("Enqueue 5 items.");
+	for (int x = 0; x < 5; x++)
+		Enqueue(&queue, x);
+	puts("Now attempting to enqueue again...");
+	Enqueue(&queue, 5.0);
+	DisplayQueue(&queue);
+	Dequeue(&queue, &value);
+	printf("Retrieved element = %f\n", value);
+	DisplayQueue(&queue);
+	Enqueue(&queue, 7.0);
+	DisplayQueue(&queue);
+	DestroyQueue(&queue);
+	return 0;
+}
diff --git a/week4/queue.c b/week4/queue.c
new file mode 100644
index 0000000..7b62294
--- /dev/null
+++ b/week4/queue.c
@@ -0,0 +1,118 @@
+/* 
+ * Authro: Walter
+ * Student ID: 1930006025
+ * Week4_queue
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include "queue.h"
+
+#include <assert.h>
+
+bool CreateQueue(Queue *queue, int size) {
+	/* do some check */
+	assert(size > 0 && "Error: szie should be positive");
+
+	/* allocate memory */
+	queue->values = (double *)malloc(sizeof(double)*size);
+	if (queue->values == NULL) {
+		return false;
+	}
+
+	/* init values */
+	queue->front = 0;
+	queue->rear = -1;
+	queue->counter = 0;
+	queue->maxSize = size;
+
+	return true;
+}
+
+bool IsEmpty(Queue *queue) {
+	return queue->counter == 0;
+}
+
+bool IsFull(Queue *queue) {
+	return queue->maxSize == queue->counter;
+}
+
+bool Enqueue(Queue *queue, double x) {
+
+	/* check full */
+	if (IsFull(queue)) {
+		fprintf(stderr, "Error: the queue is full.\n");
+		return false;
+	}
+
+	/* move rear, add counter */
+	queue->rear++;
+	queue->counter++;
+	if (queue->rear >= queue->maxSize) {
+		queue->rear = 0;
+	}
+
+	/* enqueue value */
+	queue->values[queue->rear] = x;
+
+	return true;
+}
+
+bool Dequeue(Queue *queue, double *x) {
+
+	/* check */
+	if (IsEmpty(queue)) {
+		return false;
+	}
+
+	/* dequeue value */
+	*x = queue->values[queue->front];
+
+	/* move front and decrease counter */
+	queue->front++;
+	queue->counter--;
+	if (queue->front >= queue->maxSize) {
+		queue->front = 0;
+	}
+
+	return true;
+}
+
+void DisplayQueue(Queue *queue) {
+	int pos = queue->front;
+
+	/* loop for counter */
+	for (int i=0; i<queue->counter; i++) {
+
+		/* print front hint */
+		if (i == 0) {
+			printf("front --> ");
+		} else {
+			printf("          ");
+		}
+
+		printf("%f", queue->values[pos]);
+
+		pos++;
+		/* set pos to zero if it gets to end */
+		if (pos >= queue->maxSize) {
+			pos = 0;
+		}
+
+		/* print end hint */
+		if (i == queue->counter - 1) {
+			printf(" <-- rear\n");
+		} else {
+			printf("\n");
+		}
+	}
+}
+
+void DestroyQueue(Queue *queue) {
+	free(queue->values);
+	/* reset values */
+	queue->counter = 0;
+	queue->maxSize = 0;
+	queue->front = 0;
+	queue->rear = -1;
+}
diff --git a/week4/queue.h b/week4/queue.h
new file mode 100644
index 0000000..f49f3b9
--- /dev/null
+++ b/week4/queue.h
@@ -0,0 +1,37 @@
+/* 
+ * Authro: Walter
+ * Student ID: 1930006025
+ * Week4_queue
+ */
+
+#include <stdbool.h>
+
+/* main queue structure */
+typedef struct {
+	double *values;
+	int front; /* last one of queue */
+	int rear; /* the newest one in queue */
+	int counter;
+	int maxSize;
+} Queue;
+
+/* create an queue */
+bool CreateQueue(Queue *queue, int size);
+
+/* check whether the queue is empty*/
+bool IsEmpty(Queue *queue);
+
+/* check whether the queue is full */
+bool IsFull(Queue *queue);
+
+/* put value into queue */
+bool Enqueue(Queue *queue, double x);
+
+/* get value from queue */
+bool Dequeue(Queue *queue, double *x);
+
+/* display queue to stdout */
+void DisplayQueue(Queue *queue);
+
+/* destroy an queue */
+void DestroyQueue(Queue *queue);