inno setup でYes/Noダイアログ

  // Ask the user a Yes/No question
  if MsgBox('Are you sure?', mbConfirmation, MB_YESNO) = IDYES then
  begin
    // user clicked Yes
  end else begin
    // user clicked No
  end;

ネタ元

• https://jrsoftware.org/ishelp/index.php?topic=isxfunc_msgbox