c++ threads execution time and executing thread in another thread - c++

Question

I have a code, and i'm testing how much time will take an executing of 10 threads.
#include <iostream>
#include <thread>
#include <chrono>
#include <time.h>
using namespace std;
void pause_thread(int n){
this_thread::sleep_for(chrono::seconds(n));
cout << "pause of " << n << " seconds ended\n";
}
int main(){
clock_t EndTime = clock();
thread threads[10];
cout << "Spawning 10 threads...\n";
for (int i = 0; i<10; ++i)
threads[i] = thread(pause_thread, i + 1);
cout << "Done spawning threads. Now waiting for them to join:\n";
for (int i = 0; i<10; ++i)
threads[i].join();
cout << "All threads joined!\n";
cout << "==================================================\n";
cout << "Time of executing threads: " << (double)(clock() - EndTime) / CLOCKS_PER_SEC << endl;
system("pause");
return 0;
}
The output is this:
Spawning 10 threads...
Done spawning threads. Now waiting for them to join:
pause of 1 seconds ended
pause of 2 seconds ended
pause of 3 seconds ended
pause of 4 seconds ended
pause of 5 seconds ended
pause of 6 seconds ended
pause of 7 seconds ended
pause of 8 seconds ended
pause of 9 seconds ended
pause of 10 seconds ended
All threads joined!
==================================================
Time of executing threads: 10.041
First question is: Why execution of the program takes 10,041 seconds if the pause between each thread is 1 second? What happened with the program and it took additional 0.041s on executing?
Second question is: Is this right way to execute thread in another thread?
threads[i] = thread(...);
Is this mean that thread is in the thread?
If not, how can it be done (to execute thread in another thread)?

Answer 1

First question is well answered by Brandon Haston's comment.
Answer to second question doesn't fit in a comment.
threads[i] = thread(...);
means that a std::thread has been created and its representative std::thread object has been assigned to a slot in your std::thread array. This raises a question I'm going to have to look into on my own later when I have a compiler to play with: What happened to the thread that was just overwritten?
Anyway, that new thread isn't inside another thread. Threads don't have any concept of ownership mutual. A process owns threads, but threads don't. A thread can start another thread. For example,
void pause_thread(int n){
this_thread::sleep_for(chrono::seconds(n));
cout << "pause of " << n << " seconds ended\n";
if (! cows_are_home)
{
thread newthread(pause_thread, 1);
newthread.detach();
}
}
Each new thread will wait about 1 second, then create a thread which will wait a second and create another thread, and this will go on until the cows come home.