Random always returning the same number

Question

I have a method that its function is to return 25 random numbers on a list:

static List<int> criarList()
{
    List<int> lista = new List<int>();
    for (int i = 0; i < 25; i++)
    {
        lista.Add(new Random().Next(0, 100));
    }
    return lista;
}

But for some reason, it only returns the same numbers, that is, all the same:

Why is this happening? How to fix?

Answer 1

The class Random uses an algorithm to generate the sequence of (pseudo)random numbers. This sequence is started on the basis of a value called Seed. Different values generate different sequences.

The builder Random() uses the system clock to obtain the Seed.

How are you to build multiple instances in a short span of time the Seed is always the same, always originating the same sequence.

Use only one instance:

static List<int> criarList()
{
    List<int> lista = new List<int>();
    var random = new Random();
    for (int i = 0; i < 25; i++)
    {
        lista.Add(random.Next(0, 100));
    }
    return lista;
}