private void buttonRand_Click(object sender, EventArgs e)
{
Evalueted = true;
string[] lexems = expression.Text.Split(SplitersOperation);
Random rand = new Random();
operat local = new operat(rand.NextDouble);
expression.Text = Apply(expression.Text, lexems.Last(), local);
}
private string Apply(string stingStart, string lexem, operat use) => $"{stingStart.TrimEnd(lexem.ToCharArray())}{ConvertToString(Math.Round(use(), 10)).Replace(',', '.')}";
