/in/foo.cc: In function 'int main()':
/in/foo.cc:9:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(i=0;i<a.length();i++){
                  ^
/in/foo.cc:10:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
          for(j=0;j<b.length();j++){
                   ^
/in/foo.cc:13:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(j==b.length()){
        ^