/in/foo.cc: In function 'int main()':
/in/foo.cc:17:16: warning: for increment expression has no effect [-Wunused-value]
  for(i=0;i>=A;i<=B)
               ~^~~
/in/foo.cc: In function 'int sn(int)':
/in/foo.cc:11:9: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return s;
         ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:23:29: warning: 's' is used uninitialized in this function [-Wuninitialized]
           if(m+3==n && sn(m)%6==0 &&sn(n)%6==0)
                        ~~~~~^~
/in/foo.cc:23:35: warning: 'n' may be used uninitialized in this function [-Wmaybe-uninitialized]
           if(m+3==n && sn(m)%6==0 &&sn(n)%6==0)
              ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
/in/foo.cc:23:42: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
           if(m+3==n && sn(m)%6==0 &&sn(n)%6==0)
                                     ~~~~~^~