/in/foo.cc: In function 'int main()':
/in/foo.cc:49:18: warning: statement has no effect [-Wunused-value]
             for(i;i<n;i++)
                  ^
/in/foo.cc:58:24: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
             ans_b = a[s];
                        ^