C# を使用した基本的な電卓プログラム

static float x, y;

protected void add_Click(object sender, EventArgs e) {
   x = Convert.ToInt32(tbResult.Text);
   tbResult.Text = "";
   y = '+';
   tbResult.Text += y;
}
protected void sub_Click(object sender, EventArgs e) {
   x = Convert.ToInt32(tbResult.Text);
   tbResult.Text = "";
   y = '-';
   tbResult.Text += y;
}
protected void mul_Click(object sender, EventArgs e) {
   x = Convert.ToInt32(tbResult.Text);
   tbResult.Text = "";
   y = '*';
   tbResult.Text += y;
}

protected void eql_Click(object sender, EventArgs e) {
   z = Convert.ToInt32(tbResult.Text);
   tbResult.Text = "";
   if (y == '/') {
      p = x / z;
      tbResult.Text += p;
      x = d;
   } else if (y == '+') {
      p = x + z;
      tbResult.Text += p;
      a = d;
   } else if (y == '-') {
      p = x - z;
      tbResult.Text += p;
      x = p;
   } else {
      p = x * z;
      tbResult.Text += p;
      x = p;
   }
}