/in/foo.cc: In function 'int main()':
/in/foo.cc:9:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<sta.size();i++)
             ~^~~~~~~~~~~
/in/foo.cc:10:16: warning: array subscript has type 'char' [-Wchar-subscripts]
        a[sta[i]]++;
                ^
/in/foo.cc:11:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<stb.size();i++)
             ~^~~~~~~~~~~
/in/foo.cc:12:16: warning: array subscript has type 'char' [-Wchar-subscripts]
        b[stb[i]]++;  
                ^