diff --git a/day7/homework/h3.c b/day7/homework/h3.c
new file mode 100644
index 0000000..7b570f5
--- /dev/null
+++ b/day7/homework/h3.c
@@ -0,0 +1,42 @@
+/*
+编写一个程序, 创建多个线程, 每个线程负责对一个共享计数器进行自增操作。要求实现线程间的互斥, 确保每个线程对计数器的自增操作是原子的, 不会出现竞争条件。
+*/
+#include <stdio.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <semaphore.h>
+
+sem_t sem;
+int number = 0;
+
+void *
+addfun(void *data)
+{
+    sem_wait(&sem);
+    number++;
+    printf("%ld 线程时, number = %d\n", pthread_self(), number);
+    sem_post(&sem);
+}
+
+int main(int argc, char const *argv[])
+{
+    sem_init(&sem, 0, 1);
+    printf("开始的 number = %d\n", number);
+
+    pthread_t t[5];
+    for (int i = 0; i < 5; i++)
+    {
+        pthread_create(&t[i], NULL, addfun, NULL);
+    }
+
+    for (int i = 0; i < 5; i++)
+    {
+        pthread_join(t[i], NULL);
+    }
+
+    printf("现在的 number = %d\n", number);
+
+    sem_destroy(&sem);
+
+    return 0;
+}