FUNCTION DateSerial

Devuelve un valor tipo fecha desde yyyy,mm,dd

---

// DateSerial(2019,1,1) regresa fecha 1/1/2019
// Primer_Dia_del_mes := DateSerial(Year(Today()), Month(Today())+ 0 ,1)  
// Ultimo_del_mes     := DateSerial(Year(Today()), Month(Today())+ 1 ,0) 

FUNCTION DateSerial (dwY, dwM, dwDay) AS DATE
 LOCAL nDia   AS INT
 LOCAL nmes   AS DWORD
 LOCAL nYear  AS DWORD

 nmes  := dwM  
 nYear := dwY 

 DO CASE
 CASE nmes > 0
  nYear += nmes/12
  nmes := nmes % 12
  IF nmes == 0
   nmes := 12
   nYear--
  ENDIF
 CASE nmes < 0
  nYear -= Abs(nmes/12)+1
  nmes := 12 - Abs(nmes) % 12
  IF nmes == 0
   nmes := 12
   nYear++
  ENDIF
 CASE nmes == 0
  nmes := 12
  nYear --
 END CASE

 nDia := INT(_cast,dwDay) -1
 
RETURN ConDate(nYear,nmes,1)+ndia