diff --git a/exercises/01_helloworld.c b/exercises/01_helloworld.c
index e6100166bcb8fd1064fc94f2bb0e1a6952ba8bd1..cc920be536287951c172cbcabdc72a01a70ecba4 100644
--- a/exercises/01_helloworld.c
+++ b/exercises/01_helloworld.c
@@ -2,7 +2,7 @@
 
 int main(){
 
-    // Print "Hello World!" to the console
+    printf("Hello, World!\n");
     
     
     
diff --git a/exercises/02_loop.c b/exercises/02_loop.c
index 3e361e61656c2d9ea05348a15fa275dcd3201b8a..73409d1bb1a4c08d014ab6e510b19468feb8b654 100644
--- a/exercises/02_loop.c
+++ b/exercises/02_loop.c
@@ -7,7 +7,9 @@
 
 int main(void)
 {
-	//TODO
+for (int i = 1; i <= 10; ++i) {
+        printf("%d\n", i);
+    }
 
 	return 0;
 }
\ No newline at end of file
diff --git a/exercises/03_nested_loops.c b/exercises/03_nested_loops.c
index d80c6903dd22e3305e35ff2bfb82f949e9975617..367eb5b97262a0b09883bbe5eee54f0f564b89d4 100644
--- a/exercises/03_nested_loops.c
+++ b/exercises/03_nested_loops.c
@@ -11,7 +11,12 @@
 
 int main(void)
 {		
-	//TODO
+for (int i = 1; i <= 9; ++i) {
+        for (int j = 1; j <= i; ++j) {
+            printf("%d*%d=%d\t", j, i, i * j);
+        }
+        printf("\n");
+    }
 
 	return 0;
 }
\ No newline at end of file
diff --git a/exercises/04_prime_number.c b/exercises/04_prime_number.c
index 28e3f5f8cd5dbb074c60d947c925a13d8918234e..77b8428995ab5b12db14b5c9b482881f96446ef3 100644
--- a/exercises/04_prime_number.c
+++ b/exercises/04_prime_number.c
@@ -10,8 +10,22 @@ int main(void)
 
 	for (i = 1; i <= 100; i++)
 	{
-		//TODO
-	}
+        int is_prime = 1; // 假设当前数字是素数
+
+        for (j = 2; j <= sqrt(i); j++)
+        {
+            if (i % j == 0)
+            {
+                is_prime = 0; // 不是素数
+                break;
+            }
+        }
+
+        if (is_prime && i > max)
+        {
+            max = i; // 更新最大素数
+        }
+    }
 
 	printf("max = %d\n", max);
 
diff --git a/exercises/05_josephus_ring.c b/exercises/05_josephus_ring.c
index 330f2045f5cda70d21728503ef40accd04cea14f..ff9703d41d5a021b3a1799c52443712f43592c81 100644
--- a/exercises/05_josephus_ring.c
+++ b/exercises/05_josephus_ring.c
@@ -1,29 +1,50 @@
 #include <stdio.h>
-
-/**
- * 给定100个人站成一圈，从第1个人开始依次报数。
- * 每数到3的人将会被淘汰，然后继续从下一个人开始报数。
- * 这个过程会一直持续，直到所有的人都被淘汰。
- * 请编写一个C语言程序来模拟这个过程，并且输出每一个被淘汰人的编号。
- * 要求：输出每一个被淘汰人的编号，每淘汰一个人输出一行，格式为："%d out \n"(每输出一次换行)
-*/
+#include <stdlib.h>
 
 #define ALL_NUM    	100 
 #define COUNT_NUM	3
-#define OUT_NUM		3
 
-/* people id array such as (1,2,3,4,5,6) */
-int people[ALL_NUM];
+// 定义循环链表节点
+struct Node {
+    int id;
+    struct Node* next;
+};
 
-int main(void)
-{
-	int left;	/* 剩余人数 */
-	int pos;	/* 当前报数位置 */
-	int step;	/* 当前报数 */
+// 创建循环链表
+struct Node* createCircle(int n) {
+    struct Node* head = NULL;
+    struct Node* prev = NULL;
+    for (int i = 1; i <= n; ++i) {
+        struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
+        newNode->id = i;
+        if (head == NULL) {
+            head = newNode;
+        } else {
+            prev->next = newNode;
+        }
+        prev = newNode;
+    }
+    prev->next = head; // 链接成循环
+    return head;
+}
 
-	//TODO
-	
-	
+// 模拟报数并淘汰
+void josephus(struct Node* head) {
+    struct Node* current = head;
+    while (current->next != current) {
+        for (int i = 1; i < COUNT_NUM; ++i) {
+            current = current->next;
+        }
+        struct Node* eliminated = current->next;
+        printf("%d out\n", eliminated->id);
+        current->next = eliminated->next;
+        free(eliminated);
+    }
+    printf("Last person standing: %d\n", current->id);
+}
 
-	return 0;
-}
\ No newline at end of file
+int main(void) {
+    struct Node* circle = createCircle(ALL_NUM);
+    josephus(circle);
+    return 0;
+}