foo.cc: In function ‘int cover(int, int)’:
foo.cc:33:12: warning: left operand of comma operator has no effect [-Wunused-value]
   33 |     return zj,yj,sj,xj;
      |            ^~
foo.cc:33:18: warning: right operand of comma operator has no effect [-Wunused-value]
   33 |     return zj,yj,sj,xj;
      |                  ^~
foo.cc:33:21: warning: right operand of comma operator has no effect [-Wunused-value]
   33 |     return zj,yj,sj,xj;
      |                     ^~