foo.cc: In function 'int M(int, int)':
foo.cc:10:11: warning: value computed is not used [-Wunused-value]
   M(a,n-1)*a;
   ~~~~~~~~^~
foo.cc:20:9: warning: 'c' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return c;
         ^
foo.cc: In function 'int main()':
foo.cc:27:34: warning: 'c' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<a<<"^"<<b<<" mod "<<c<<"="<<h;
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~

[Hydro](https://hydro.ac)提供评测服务