i can not add computer in ti tac toe

Question

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

namespace WindowsFormsApp7

{

public partial class Form1 : Form

{

public Form1()

{

InitializeComponent();

}

public int s1;

public int s2;

public int sd;

public int turns = 0;

public bool onturn = true;

public Button CPU()

{

Button button = null;

button = CPUtrywinordefend("O");

if (button != null)

return button;

else

{

button = CPUtrywinordefend("X");

if (button != null)

return button;

else

return CPUmoverandom();

}

}

public Button CPUtrywinordefend(string s)

{

Button button = null;

//horizonatl

if ((button1.Text) == (button2.Text) && button1.Text == s && button3.Text == "")

return button3;

else if (button1.Text == button3.Text && button1.Text == s && button2.Text == "")

return button2;

else if (button2.Text == button3.Text && button2.Text == s && button1.Text == "")

return button1;

else if ((button4.Text) == (button6.Text) && button4.Text == s && button5.Text == "")

return button5;

else if (button4.Text == button5.Text && button4.Text == s && button3.Text == "")

return button2;

else if (button6.Text == button5.Text && button5.Text == s && button4.Text == "")

return button4;

else if (button7.Text == button9.Text && button7.Text == s && button8.Text == "")

return button8;

else if (button7.Text == button8.Text && button7.Text == s && button9.Text == "")

return button9;

else if (button9.Text == button8.Text && button9.Text == s && button7.Text == "")

return button7;

//vertikall

else if ((button1.Text) == (button4.Text) && button1.Text == s && button7.Text == "")

return button7;

else if (button1.Text == button7.Text && button1.Text == s && button4.Text == "")

return button4;

else if (button7.Text == button4.Text && button4.Text == s && button1.Text == "")

return button1;

else if (button8.Text == button5.Text && button5.Text == s && button2.Text == "")

return button2;

else if (button8.Text == button2.Text && button2.Text == s && button5.Text == "")

return button4;

else if (button2.Text == button5.Text && button2.Text == s && button8.Text == "")

return button8;

else if (button9.Text == button6.Text && button6.Text == s && button3.Text == "")

return button3;

else if (button9.Text == button3.Text && button3.Text == s && button6.Text == "")

return button6;

else if (button3.Text == button6.Text && button2.Text == s && button9.Text == "")

return button9;

//diagonal9.Text == "")

else if (button1.Text == button5.Text && button5.Text == s && button9.Text == "")

return button9;

else if (button9.Text == button1.Text && button9.Text == s && button5.Text == "")

return button5;

else if (button9.Text == button5.Text && button5.Text == s && button1.Text == "")

return button1;

else if (button7.Text == button5.Text && button5.Text == s && button3.Text == "")

return button3;

else if (button7.Text == button3.Text && button3.Text == s && button5.Text == "")

return button5;

else if (button3.Text == button5.Text && button5.Text == s && button7.Text == "")

return button7;

else return null;

}

public Button CPUmoverandom()

{

Button button = null;

foreach (Control C in Controls)

{

button = C as Button;

if (button != null)

{

if (button.Text == "")

return button;

}

}

return null;

}

private void buttonclicked(object sender, EventArgs e)

{

Button button = (Button)sender;

{

if (button.Text == "")

{

if (onturn == true)

button.Text = "X";

else

button.Text = "O";

turns++;

onturn = !onturn;

}

if (CheckWinner() == true)

{

if (onturn == false)

{

s1++;

MessageBox.Show("??? ?????");

newgame();

if (onturn == false) ;

}

else

{

s2++;

MessageBox.Show("??????????? ?????");

newgame();

}

}

if (Checkdraw() == true && CheckWinner() == false)

{

sd++;

MessageBox.Show("fre");

newgame();

}

if(onturn== false)

{

CPU().PerformClick();

}

}

}

public void newgame()

{

button1.Text = button2.Text = button3.Text = button4.Text = button5.Text = button6.Text = button7.Text = button8.Text = button9.Text = "";

turns = 0;

onturn = true;

label1.Text = s1.ToString();

label2.Text = s2.ToString();

label3.Text = sd.ToString();

}

public bool Checkdraw()

{

if ((turns == 9) && CheckWinner() == false)

return true;

else

return false;

}

public bool CheckWinner()

{

//?????????????

if ((button1.Text == button2.Text) && (button2.Text == button3.Text) && button1.Text != "")

return true;

else if ((button4.Text == button5.Text) && (button5.Text == button6.Text) && button4.Text != "")

return true;

else if ((button7.Text == button8.Text) && (button8.Text == button9.Text) && button7.Text != "")

return true;

// ???????????

if ((button1.Text == button4.Text) && (button4.Text == button7.Text) && button1.Text != "")

return true;

else if ((button2.Text == button5.Text) && (button5.Text == button8.Text) && button2.Text != "")

return true;

else if ((button3.Text == button6.Text) && (button6.Text == button9.Text) && button3.Text != "")

return true;

// ???????????

if ((button1.Text == button5.Text) && (button5.Text == button9.Text) && button1.Text != "")

return true;

else if ((button3.Text == button5.Text) && (button5.Text == button7.Text) && button3.Text != "")

return true;

else

return false;

}

private void button11_Click(object sender, EventArgs e)

{

s1 = s2 = sd = 0;

newgame();

}

private void button10_Click(object sender, EventArgs e)

{

newgame();

}

private void button12_Click(object sender, EventArgs e)

{

}

private void Form1_Load(object sender, EventArgs e)

{

label1.Text= "X :" + s1;

label2.Text = "O:" + s2;

label3.Text = "fre:" + sd;

}

}

}