foo.cc: In function 'node* unique(node*)':
foo.cc:70:22: warning: left operand of comma operator has no effect [-Wunused-value]
   70 |         for (;p->next!=NULL,p!=NULL;p=p->next)
      |                      ^
foo.cc: In function 'node* setunion(node*, node*, node*)':
foo.cc:103:31: warning: left operand of comma operator has no effect [-Wunused-value]
  103 |                 for (j=head3;j!=NULL,j!=prev;j=j->next)
      |                               ^
foo.cc:102:21: warning: unused variable 'flag' [-Wunused-variable]
  102 |                 int flag=0;
      |                     ^~~~

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