resource – .h file:

#define CustomAlert 1000

resource – .rcp file:

ALERT ID CustomAlert
BEGIN
  TITLE "custom alert"
  MESSAGE "^1\n^2\n^3"
  BUTTONS "OK"
END

code:

Char alertMsg[64];
StrPrintF(alertMsg, "Your value is %d", yourValue);
FrmCustomAlert(CustomAlert, alertMsg, "", "");

do NOT pass NULL value as param in FrmCustomAlert – always use ””.