foo.cc: In member function 'Bigint& Bigint::Add(Bigint&)':
foo.cc:85:10: warning: reference to local variable 'ans' returned [-Wreturn-local-addr]
   85 |   return ans;
      |          ^~~
foo.cc:62:10: note: declared here
   62 |   Bigint ans;
      |          ^~~
foo.cc: In member function 'Bigint& Bigint::Mul(Bigint&)':
foo.cc:110:10: warning: reference to local variable 'ans' returned [-Wreturn-local-addr]
  110 |   return ans;
      |          ^~~
foo.cc:89:10: note: declared here
   89 |   Bigint ans;
      |          ^~~
foo.cc: In member function 'bool Bigint::operator>(Bigint&)':
foo.cc:138:2: warning: control reaches end of non-void function [-Wreturn-type]
  138 |  }
      |  ^

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