//ShowMessage:
begin ShowMessage('提示内容');      {标题默认工程名, 如: Proect1}

  Application.Title := '警告';  {如果修改工程标题...}
  ShowMessage('提示内容');      {标题是'警告'}

  ShowMessage('第一行' + #13#10 + '第二行');  {提示信息换行}
  ShowMessage('第一行'#13'第二行');     {也可以}
end;

//InputBox:
var
  s: string;
begin
  s := InputBox('标题','提示信息','默认输入');
  ShowMessage(s);  //显示输入的内容
end;

//InputQuery:
var
  s: string;
begin
  InputQuery('标题','提示信息',s);  //为字符串变量 S 输入值, 返回布尔型
  ShowMessage(s);  //显示输入的内容
end;

//MessageBox:
var
  i: Integer;
begin
  i := MessageBox(0,'提示内容','标题',mrOk);  //第一个参数一般用 Self.Handle, 0代表桌面

  //可选参数
  //mrNone
  //mrOk
  //mrCancel
  //mrAbort
  //mrRetry
  //mrIgnore
  //mrYes
  //mrNo
  //mrAll
  //mrNoToAll
  //mrYesToAll

  ShowMessage(IntToStr(i));

  //还可以组合第四个参数以调用不同的图标:
  MessageBox(0,'提示内容','标题',mrOk + MB_ICONHAND);

  //MB_ICONHAND
  //MB_ICONQUESTION
  //MB_ICONEXCLAMATION
  //MB_ICONASTERISK
  //MB_USERICON
  //MB_ICONWARNING
  //MB_ICONERROR
  //MB_ICONINFORMATION
  //MB_ICONSTOP
end;

//后来补充, 还是应该使用 API 的原有参数更好些:
{可选参数或它们的组合}
MB_OK                        = $00000000;
MB_OKCANCEL                  = $00000001;
MB_ABORTRETRYIGNORE          = $00000002;
MB_YESNOCANCEL               = $00000003;
MB_YESNO                     = $00000004;
MB_RETRYCANCEL               = $00000005;
MB_ICONHAND                  = $00000010;
MB_ICONQUESTION              = $00000020;
MB_ICONEXCLAMATION           = $00000030;
MB_ICONASTERISK              = $00000040;
MB_USERICON                  = $00000080;
MB_ICONWARNING               = MB_ICONEXCLAMATION;
MB_ICONERROR                 = MB_ICONHAND;
MB_ICONINFORMATION           = MB_ICONASTERISK;
MB_ICONSTOP                  = MB_ICONHAND;
MB_DEFBUTTON1                = $00000000;
MB_DEFBUTTON2                = $00000100;
MB_DEFBUTTON3                = $00000200;
MB_DEFBUTTON4                = $00000300;
MB_APPLMODAL                 = $00000000;
MB_SYSTEMMODAL               = $00001000;
MB_TASKMODAL                 = $00002000;
MB_HELP                      = $00004000;
MB_NOFOCUS                   = $00008000;
MB_SETFOREGROUND             = $00010000;
MB_DEFAULT_DESKTOP_ONLY      = $00020000;
MB_TOPMOST                   = $00040000;
MB_RIGHT                     = $00080000;
MB_RTLREADING                = $00100000;
MB_SERVICE_NOTIFICATION      = $00200000;
MB_SERVICE_NOTIFICATION_NT3X = $00040000;
MB_TYPEMASK                  = $0000000F;
MB_ICONMASK                  = $000000F0;
MB_DEFMASK                   = $00000F00;
MB_MODEMASK                  = $00003000;
MB_MISCMASK                  = $0000C000;

{可能的返回值}
IDOK       = 1;   ID_OK = IDOK;
IDCANCEL   = 2;   ID_CANCEL = IDCANCEL;
IDABORT    = 3;   ID_ABORT = IDABORT;
IDRETRY    = 4;   ID_RETRY = IDRETRY;
IDIGNORE   = 5;   ID_IGNORE = IDIGNORE;
IDYES      = 6;   ID_YES = IDYES;
IDNO       = 7;   ID_NO = IDNO;
IDCLOSE    = 8;   ID_CLOSE = IDCLOSE;
IDHELP     = 9;   ID_HELP = IDHELP;
IDTRYAGAIN = 10;
IDCONTINUE = 11;

//MessageDlg:
var
  i: Integer;
begin
  MessageDlg('提示信息',mtWarning,mbYesNo,0);

  //第二个参数调用不同的图标:
  //mtWarning
  //mtError
  //mtInformation
  //mtConfirmation
  //mtCustom

  //第三个参数调用不同的按钮:
  //mbYesNo = [mbYes, mbNo];
  //mbYesNoCancel = [mbYes, mbNo, mbCancel];
  //mbYesAllNoAllCancel = [mbYes, mbYesToAll, mbNo, mbNoToAll, mbCancel];
  //mbOKCancel = [mbOK, mbCancel];
  //mbAbortRetryIgnore = [mbAbort, mbRetry, mbIgnore];
  //mbAbortIgnore = [mbAbort, mbIgnore];
  //可以直接输入集合元素,譬如: MessageDlg('aaa',mtWarning,[mbYes],1);

  //第四个参数帮助ID, 没有添0
  //还有重载的第5个参数是设定默认按钮
  //如果要本地话显示需要修改源文件, 一般可以用 MessageBox 代替
end;

//MessageDlgPos:
begin
  MessageDlgPos('提示信息',mtCustom,mbYesNoCancel,0,400,100);
  //比 MessageDlg 多出两个参数来控制显示位置
end;