foo.cc: In function 'int main()':
foo.cc:48:16: warning: unused variable 'c' [-Wunused-variable]
  long long a,b,c[10];
                ^
foo.cc: In function 'long long int ab(long long int, long long int)':
foo.cc:30:16: warning: 'f' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return ac(c,10); 
                ^
foo.cc: In function 'long long int ac(long long int*, long long int)':
foo.cc:44:9: warning: 'f' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return f;
         ^

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。