foo.cc: In function 'void sb(int, int)':
foo.cc:13:9: warning: 'xx' is used uninitialized in this function [-Wuninitialized]
   if(x>0&&x<n+1&&y>0&&y<n+1){
      ~~~^~~~~~~
foo.cc:27:6: note: 'xx' was declared here
  int xx,yy;
      ^~

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