c++中的多线程......如何执行

我在tutorialspoint.com上学习c++中的多线程，在那里我发现了以下代码：

#include<iostream>
#include<cstdlib>
#include<pthread.h>
using namespace std;
#define NUM_THREADS 5
void *PrintHello(void *threadnum)
{
    long int *tnum;
    tnum=(long*)threadnum;
    cout<<"Hello World! Thread num:"<<tnum<<endl;
    pthread_exit(NULL);
}
int main()
{
    pthread_t threads[NUM_THREADS];
    int rc;
    long int i;
    for(i=0;i<NUM_THREADS;i++)
    {
        cout<<"main(): creating thread,"<<i<<endl;
        rc=pthread_create(&threads[i],NULL,PrintHello,(void*)i);
        cout<<"Thread ID:"<<threads[i]<<endl;
        cout<<"-----------------------------------------------"<<endl;
        if(rc)
        {
            cout<<"Error:Unable to create thread,"<<rc<<endl;
            exit(-1);
        }
    }
    pthread_exit(NULL);
}

当我编译这个代码时，我得到的输出是：

main(): creating thread,0
Thread ID:124028821706496
-----------------------------------------------
main(): creating thread,1
Thread ID:124028812797696
-----------------------------------------------
main(): creating thread,2
Hello World! Thread num:0
Thread ID:124028803434240
-----------------------------------------------
main(): creating thread,3
Hello World! Thread num:0x1
Hello World! Thread num:Thread ID:0x20x70cdb43d6700
-----------------------------------------------
main(): creating thread,4
Thread ID:124028785452800
Hello World! Thread num:0x4
-----------------------------------------------
Hello World! Thread num:0x3

我的疑问是为什么我会得到这种输出，我指的是

cout<<"Hello World! Thread num:"<<tnum<<endl;

为什么这个语句没有按顺序执行。应该做什么更改？？有人能帮我吗？？