title: How to disable button if textbox is empty
body: <p>First of all sorry for my bad english.
  I'm beginner at C# and i made a Windows forms application but i can't disable one button if a textbox is empty.
  I tried some of the Enabled methods but they didn't work. Hope someone can help me fix this. Thank you very much</p>
  
  <pre><code>public partial class ModulusForm : Form
  {
      public double nje;
      public double dy;
      public double pergjigja;
      public double rezultati;
      public ModulusForm()
      {
  
          InitializeComponent();
          Button btn = new Button();
          btn.Click += new EventHandler(butoniGjenero_Click); 
      }
      private void butoniPerfundo_Click(object sender, EventArgs e)
      {
          this.Close();
      }
      private void butoniGjenero_Click(object sender, EventArgs e)
      {
          Random random = new Random();
          nje = random.Next(1, 100);
          dy = random.Next(1, 100);
          if (nje &gt; dy)
          { textboxPyetja.Text = "X = " + nje + "    " + "dhe" + "    " + "Y = " + dy; }
          else if (nje &gt; dy)
          {
              nje = random.Next(1, 100);
              dy = random.Next(1, 100);
          }
          rezultati = nje / dy;
      }
      private void butoniPastro_Click(object sender, EventArgs e)
      {
              textboxPyetja.Clear();
              textboxPergjigja.Clear();
              textboxPergjigjaSakt.Clear();
      }
      private void butoniVerteto_Click(object sender, EventArgs e)
      {
          try
          {
              pergjigja = double.Parse(textboxPergjigja.Text);
          }
          catch
          {
              var informim = MessageBox.Show("Rishiko fushat!", "Verejtje", MessageBoxButtons.OK, MessageBoxIcon.Information);
          }
          if (textboxPergjigja.Text == "")
          {
              //nothin' baby
          }
          else
          {
              if (textboxPyetja.Text == "")
              {
                  var informim = MessageBox.Show("Fusha e pyetjes eshte null!", "Verejtje", MessageBoxButtons.OK, MessageBoxIcon.Information);
              }
              else
              {
                  if (pergjigja == rezultati)
                  {
                      textboxPergjigjaSakt.Text = "Pergjigja eshte e sakte";
                  }
                  else
                  {
                      textboxPergjigjaSakt.Text = "Gabim." + " " + "Pergjigja e sakte eshte: " + "" + rezultati;
                  }
                  comboboxVargu.Items.Add(nje + " / " + dy + " = " + rezultati);
              }
          }
      }
  }
  </code></pre>
  
  <p>}</p>