Question

I was experimenting with tasks. Why does this output 10 and not each value of the loop?

public static void StartTasks()
{
    Task[] tasks = new Task[10];
    for (int i = 0; i < 10; i++)
        tasks[i] = new Task(() => Console.WriteLine(i));

    foreach (Task task in tasks)
    {
        task.Start();                       
    }       
}

Answer 1

C# lambdas capture a reference to the variable, not the value of the variable.

If you want to capture the value, you need to make a copy of it first inside the loop which causes the capture to get the reference to the locally scoped unchanging variable.

public static void StartTasks()
{
    Task[] tasks = new Task[10];
    for (int i = 0; i < 10; i++) {
        int j = i;
        tasks[i] = new Task(() => Console.WriteLine(j));
    }

    foreach (Task task in tasks)
    {
        task.Start();                       
    }       
}