foo.cc: In function 'int main()':
foo.cc:9:18: warning: unused variable 'j' [-Wunused-variable]
  long long a,b,i,j,y;
                  ^
foo.cc:21:20: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<a/b<<"/"<<y/b;
                    ^

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