Generate Random Password in ASP.NET and C#.net

protected void Button1_Click(object sender, EventArgs e)

    {

        string allowedChars = "";

        allowedChars = "a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,";

        allowedChars += "A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,";

        allowedChars += "1,2,3,4,5,6,7,8,9,0,!,@,#,$,%,&,?";

        char[] sep = { ',' };

        string[] arr = allowedChars.Split(sep);

        string passwordString = "";

        string temp = "";

        Random rand = new Random();

        for (int i = 0; i < Convert.ToInt32(txtPassLength.Text); i++)

        {

            temp = arr[rand.Next(0, arr.Length)];

            passwordString += temp;

        }

        txtpassword.Text = passwordString;

    }