来自链接 https://bbs.csdn.net/topics/390689473?page=1

private void button1_Click(object sender, EventArgs e)
{
    Random r = new Random();
    double a = 1.3;
    double b = 1.4;
    var next = r.NextDouble() * (b - a);
    next += a;
    MessageBox.Show(next.ToString());
}