Update printf ("AAABBBCCC')

README.md

@@ -1,2 +1,42 @@
-# os1
+
+#include <stdio.h>   
+#include <stdlib.h>   
+#include <pthread.h>   
+#include <unistd.h>   
+#include <sys/types.h>   
+#include <semaphore.h> 
+sem_t A,B;
+void* p1(void *arg){
+	for(int i=0;i<10;i++){
+	printf("A\n");
+	}
+    sem_post(&A);
+} 
+void* p2(void *arg){
+    sem_wait(&A);
+	for(int i=0;i<10;i++){
+	printf("B\n");
+	}
+    sem_post(&B);
+} 
+void* p3(void *arg){
+    sem_wait(&B);
+	for(int i=0;i<10;i++){
+	printf("C\n");
+	}
+    
+} 
+
+int main()  
+{
+sem_init(&A,0,0);
+sem_init(&B,0,0);
+	pthread_t tid[3];  
+	pthread_create(&tid[0], NULL, p1, NULL);  
+	pthread_create(&tid[1], NULL, p2, NULL);  
+	pthread_create(&tid[2], NULL, p3, NULL);  
+	for(int i = 0; i < 3; i++)  
+		pthread_join(tid[i], NULL);      
+	printf("main is over\n");
+}