Private Sub button1_Click(sender As Object, e As System.EventArgs)
    If textBox1.Text = "" Then
        MessageBox.Show("You must enter a name.", "Name Entry Error", _
           MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
    Else
        ' Code to act on the data entered would go here.
    End If
End Sub

private void button1_Click(object sender, System.EventArgs e) {
   if(textBox1.Text == "") {
      MessageBox.Show("You must enter a name.", "Name Entry Error",
         MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
   }
   else {
      // Code to act on the data entered would go here.
   }
}

private:
   void button1_Click( Object^ sender, System::EventArgs^ e )
   {
      if ( textBox1->Text->Equals( "" ) )
      {
         MessageBox::Show( "You must enter a name.", "Name Entry Error",
            MessageBoxButtons::OK, MessageBoxIcon::Exclamation );
      }
      else
      {
         // Code to act on the data entered would go here.
      }
   }