foo.cc: In member function 'BigInt BigInt::Mul(int)':
foo.cc:41:3: warning: no return statement in function returning non-void [-Wreturn-type]
   41 |   }
      |   ^
foo.cc: In member function 'BigIntArray& BigIntArray::Cin(char*)':
foo.cc:85:17: warning: comparison of integer expressions of different signedness: 'int' and 'size_t' {aka 'long unsigned int'} [-Wsign-compare]
   85 |    for(int j=0;j<strlen(s);j++)
      |                ~^~~~~~~~~~
foo.cc:84:8: warning: unused variable 'i' [-Wunused-variable]
   84 |    int i=n;
      |        ^

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