/in/foo.cc: In function 'int main()':
/in/foo.cc:60:26: warning: unused variable 'a3' [-Wunused-variable]
  int a1[10000],a2[10000],a3[10000];
                          ^~
/in/foo.cc: In function 'void MergeSubs(int*, int)':
/in/foo.cc:40:10: warning: 'flag' may be used uninitialized in this function [-Wmaybe-uninitialized]
    flag++;
          ^