grep regex containing 'yyy' but not containing 'zzz' :

1. First, finding all files containing 'yyy', and keep in one file

grep -r -l "yyy" /c/folder/ > grepsearch.txt

1. Second, call this script : grepsearch.sh who is looping on first result file and search number of occurencies of the second search 'zzz'

for file in `cat grepsearch.txt`; do 
   # echo "---------------------------------------------------------- $file"; 
   grepcount=$(grep -c 'zzz' $file); 
#   echo $grepcount $file; 
   if [ $grepcount -eq 0 ]
   then
#      echo "No matching search zzz";
      echo $file;
#   else
#      echo "Match search zzz";
   fi
done

Note : if your search contain "\" add a second : "\\"