error in the implementation of my method in my wcf project

Question

Hi,
when i implement the method MiseAjourEtatFactureWCF(ref string REF_COMPTE_FACTURATION, ref int STATUT) in my wcf project this following error has appeared:

error:
Invalid expression term 'if'

code:

 public retour 
MiseAjourEtatFactureWCF(ref string REF_COMPTE_FACTURATION, ref int 
STATUT)
{
Service1 ser = new 
Service1();
retour rt = new 
retour();
ser.MiseAJourFacture(
if
 (ser.MiseAjourEtatFacture(REF_COMPTE_FACTURATION,STATUT).Equals(-1))
{
try
{
rt.CodeRetour = -1;
rt.msgRetour
 = "mise à 
jour etat facture échoué";
}
catch
 (Exception e)
{
CreateLog log = new
 CreateLog(e);

log.ErrorLog(@"C:\Documents and 
Settings\Administrateur\Bureau\fichierLog.txt");
}

return rt;
}
else
{
rt.CodeRetour = 0;
rt.msgRetour =
 "mise à jour
 etat facture réussit";
return
 rt;
}
}

knowing that the goal of this method is to return error an message and to create log file in the case of failed call of the method
MiseAjourEtatFacture(REF_COMPTE_FACTURATION,STATUT) and the succes message in the case of succeeded call of this method.


Please help me because i'm a beginner. :((((((((((