title: Delete all non-digits from textbox
body: <p>I have textbox1 where i enter number. Example: 123
  I also have textbox2 where the sum is shown. Example: 6 (1+2+3)</p>
  
  <p>What i need is. If there is only numbers in my textbox1, then everything is fine and i'm getting sum.
  If there is something more than numbers like 1a2b3c i want the programm to show message box with Warning and a text. Delete all non-digits? If the guy press Yes, then it does delete abc and only 123 is left. If no, then Error shows up.</p>
  
  <p>My code: </p>
  
  <pre><code> private void button1_Click(object sender, EventArgs e)
      {
  
          int cipari = Convert.ToInt32(textBox1.Text);
  
          int summa = 0;
          for (int n = cipari; n &gt; 0; summa += n % 10, n /= 10) ;
  
          DialogResult dialogResult = MessageBox.Show("Delete all non-digits?", "Warning", MessageBoxButtons.YesNo);
          if (dialogResult == DialogResult.Yes)
          {
              textBox2.Text = summa.ToString();
          }
          else if (dialogResult == DialogResult.No)
          {
              textBox2.Text = "Error! You can't sum non-digits!";
          }
  
  
      }
  </code></pre>