/in/foo.cc: In function 'void pus()':
/in/foo.cc:24:8: warning: unused variable 'j' [-Wunused-variable]
  int i,j,k=0;
        ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:66:12: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
     else if(n==2) 
            ^
/in/foo.cc:99:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<s.size();++i)
          ~^~~~~~~~~