/in/foo.cc: In function 'int main()':
/in/foo.cc:24:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |                 for(int j=0;j<s1.size();j++)
      |                             ~^~~~~~~~~~
/in/foo.cc:26:28: error: 'a' was not declared in this scope
   26 |                         if(a[j-1]!=a[j] && a[j+1]!=a[j])
      |                            ^