Some confusion about POSIX threads

[manasij7479]

I decided to learn threading for a program of mine which seems (I may be wrong) to scream its necessity.
I thought threads were supposed to be executed in parallel in machines having more than one core.
So why am I getting the following output from the following program?
[I left out joining for now...Does that play a role here ?]

#define _REENTRANT
#include<pthread.h>
#include<iostream>
using namespace std;

void* foo(void* arg);
int main()
{
    int return_value;
    pthread_t reference;
    return_value= pthread_create(&reference,NULL,foo,NULL);
    if(return_value!=0)
    {
        cout<<"Creation Failed";
        return 1;
    }
    int x(10);
    while(x--)
        cout<<8;
    
                
    return 0;
    
}
void* foo(void* arg)
{
    //cout<<"Thread Running.."<<endl;
    int x(10);
    
    while(x--)
        cout<<9;
    return (void*)(arg);
}

The output is

99999999998888888888

instead of my expected jumble of 9s and 8s. Why is it so ?

[MK27]

You want to use pthread_detach() after pthread_create.

Also: there are no guarantees about the order of events with separate threads. Do not even presume that you will get:

98989898989

You are just as likely to get 999999888888 again, or 888888999999. If you need to guarantee a sequence, you will need to use mutex locks. Without locking, threads are fine for doing things that do not have to happen in any particular order (because they won't).