foo.cc: In function 'int main()':
foo.cc:64:8: error: 'i' was not declared in this scope
  for(  i=1; i<a.size(); i++){
        ^
foo.cc:19:15: warning: unused variable 'y' [-Wunused-variable]
  long int j,k,y=0;
               ^

自豪的采用jd5进行评测(github.com/masnn/jd5)