foo.cc: In function 'sum* UN(sum*)':
foo.cc:58:24: warning: left operand of comma operator has no effect [-Wunused-value]
   58 |         for (;pro->next!=NULL,pro!=NULL;pro=pro->next)
      |                        ^
foo.cc: In function 'sum* setunion(sum*, sum*, sum*)':
foo.cc:88:28: warning: left operand of comma operator has no effect [-Wunused-value]
   88 |                 for (i=h3;i!=NULL,i!=PRE;i=i->next)
      |                            ^
foo.cc:87:21: warning: unused variable 'flag' [-Wunused-variable]
   87 |                 int flag=0;
      |                     ^~~~

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