/in/foo.cc: In function 'int main()':
/in/foo.cc:32:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (j=s-1,k=t-1;j<st.size() && k<st.size(); j++,k++) {
                     ~^~~~~~~~~~
/in/foo.cc:32:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (j=s-1,k=t-1;j<st.size() && k<st.size(); j++,k++) {
                                    ~^~~~~~~~~~