Why does Thread work like this?

Question

C++ / C#

for (int i = 0; i < 2; i++)
            {
                Thread thread = new Thread(() =>
                {
                    Console.WriteLine("main index: " + i);
                  
                });
                thread.Start();
            }

Why is the output:
main index: 2
main index: 2

Where are the values ​​0.1?

Answer 1

It's not the thread's fault, it's the closures .
When you refer to a variable in a lambda, it is accessed by reference.
So it turned out that at the time of launch, the value of i is already 2. You
can solve this problem if you copy the value of i into a new variable like this:

for (int i = 0; i < 2; i++)
{
    var i2 = i;
    Thread thread = new Thread(() =>
    {
        Console.WriteLine("main index: " + i2);
    });
    thread.Start();
}