How to use if, else in sql server

this my cod in sql server

IF (#fldlist.fldid# >  0 )
            update TblTestMalle set fldnamcod=#fldnamcod# ,fldmal=#fldmal#,flddate=#flddate# , fldmodl=#fldmodl# where fldid=#fldlist.fldid#

else
insert into TblTestMalle (fldnamcod,fldmal,fldmodl,flddate)
    select #fldnamcod#   , #fldmal# , #fldmodl# , #flddate#

and my error is

exec sp_executesql N'IF (#fldlist.fldid# >  0 )
            update TblTestMalle set fldnamcod=@fldnamcod ,fldmal=@fldmal,flddate=@flddate , fldmodl=@fldmodl where fldid=#fldlist.fldid#

else
insert into TblTestMalle (fldnamcod,fldmal,fldmodl,flddate)
    select @fldnamcod   , @fldmal , @fldmodl , @flddate',N'@fldnamcod nvarchar(2),@fldmal nvarchar(2),@fldmodl nvarchar(2),@flddate nvarchar(9)',@fldnamcod=N'13',@fldmal=N'13',@fldmodl=N'13',@flddate=N'1398/8/13' 

know how can i do ???