C# - How to create yes-no question

..last parameter is default button (=second button in dialog).

if ( MessageBox.Show( this, "All data will be deleted. Continue ?",
     "Question", MessageBoxButtons.YesNo, MessageBoxIcon.Question, 
     MessageBoxDefaultButton.Button2 ) == DialogResult.No ) return;

Output:

C# - How to show the most easy message box

MessageBox.Show( "This is a message.." );

Output: