/in/foo.cc: In function 'int main()':
/in/foo.cc:818:31: error: no 'operator++(int)' declared for postfix '++' [-fpermissive]
  818 |         for(Bigint i=1;i<=n1;i++)
      |                              ~^~
/in/foo.cc:820:31: error: no 'operator++(int)' declared for postfix '++' [-fpermissive]
  820 |         for(Bigint i=1;i<=n2;i++)
      |                              ~^~
/in/foo.cc: At global scope:
/in/foo.cc:458:20: warning: 'std::string std::to_string(int)' defined but not used [-Wunused-function]
  458 | static std::string to_string(const int value)
      |                    ^~~~~~~~~