Forgetting to join a thread or detach it (make it unjoinable) before the main program terminates, will cause in a program crash.

For example, the t1 thread is not joined to the main thread.

#include <iostream>
#include <thread>
using namespace std;
 
 
void HelloWorld()
{
  cout << "Hello World" << endl;
}
 
 
int main()
{
  thread t1(HelloWorld);
  //t1.join();  // If the thread is not joined to the main thread it will cause a crash.
  return 0;
}