线程执行顺序

#include<stdio.h>
#include<pthread.h>
void thread(void)
{
int i;
for(i=0;i<10;i++){
sleep(1);
printf("this is %d pthread\n,i");
}
}
int main(void)
{
pthread_t id;
int i,ret;
ret = pthread_creat(&id,NULL,(void*)thread,NULL);
if(ret!=0){
printf("creat error");
exit(1);
}
for(i=0;i<10;i++)
{
sleep(1);
printf("this is the main thread\n");
pthread_join(id,NULL);
return 0;
}
}
执行结果为
this is the main thread
this is 0 pthread
this is the main thread
this is 1 pthread
this is the main thread
this is 2 pthread
this is the main thread
this is 3 pthread
this is the main thread
this is 4 pthread
this is the main thread
this is 5 pthread
this is the main thread
this is 6 pthread
this is the main thread
this is 7 pthread
this is the main thread
this is 8 pthread
this is the main thread
this is 9 pthread
可见主进程创建线程时先运行进程

lz的解释和我运行的有出入：

代码：
#include<stdio.h>
#include<pthread.h>
#include<unistd.h>
#include<stdlib.h>
void thread(void)
{
int i;
for(i=0;i<10;i++){
sleep(1);
printf("this is %d pthread\n",i);
}
}
int main(void)
{
pthread_t id;
int i,ret;
ret = pthread_create(&id,NULL,(void*)thread,NULL);
if(ret!=0){
printf("creat error");
exit(1);
}
for(i=0;i<10;i++)
{
sleep(1);
printf("this is the main thread\n");
//pthread_join(id,NULL);
return 0;
}
}

执行效果
this is 0 pthread
this is the main thread

分析：
按lz说法，屏蔽掉pthread_join(id,NULL);
的话，应该执行不到线程，直接返回退出了，但执行效果不是。
主程序进程执行到
sleep(1);
printf("this is the main thread\n");
sleep这句时，并没执行printf("this is the main thread\n");
而是去执行线程了，执行完线程中的输出，在线程sleep时才又回到进程中，并return，结束，所以有上面的结果，不想lz说的那样，主进程创建线程时先运行进程。

而加上pthread_join(id,NULL);
这句的时候，执行效果是
this is the main thread
this is 0 pthread
this is 1 pthread
this is 2 pthread
this is 3 pthread
this is 4 pthread
this is 5 pthread
this is 6 pthread
this is 7 pthread
this is 8 pthread
this is 9 pthread
分析：先执行了一次主进程中的printf("this is the main thread\n");
之后，遇到pthread_join(id,NULL);
这句，进而转去执行线程中内容，输出后，虽然遇到sleep（1），但此时的sleep也只是为其他进程让cpu，主进程由于执行了pthread_join(id,NULL);
会一直等它要等的这个线程退出以后才继续往下执行。直到线程中的i=10，线程退出，结束pthread_join(id,NULL);
，继续往下执行主进程中内容，而此时主进程只有return 0了，所以返回退出，才出现如上所述效果。
为什么会和lz同一个程序出校不同的执行效果呢？
求一个权威的解答！！！！