Why does my thread not run in background?

In the listing bellow, I expect that as I call t.detach() right after the line when the thread is created, the thread t will run in background while the printf("quit the main function now \n") will called and thenmain will exit.

#include <thread>
#include <iostream>

void hello3(int* i)
{

    for (int j = 0; j < 100; j++)
    {
        *i = *i + 1;
        printf("From new thread %d \n", *i);
        fflush(stdout);

    }

    char c = getchar();
 }

int main()
{
    int i;
    i = 0;
    std::thread t(hello3, &i);
    t.detach();
    printf("quit the main function now \n");
    fflush(stdout);
    return 0;
}

However from what it prints out on the screen it is not the case. It prints

From new thread 1
From new thread 2
....
From new thread 99
quit the main function now.

It looks like the main function waits until the thread finishes before it executes the commandprintf("quit the main function now \n"); and exits.

Can you please explain why it is? What I am missing here?