/in/foo.cc: In function 'int main()':
/in/foo.cc:90:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(i < s.size()){
         ~~^~~~~~~~~~
/in/foo.cc:93:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
       while(i<s.size() && isdigit(s[i])){
             ~^~~~~~~~~
/in/foo.cc: In function 'int cal(Node*)':
/in/foo.cc:83:14: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
   return ans%MOD;
              ^~~