/in/foo.cc: In function 'int sum(int*, int, int)':
/in/foo.cc:5:11: warning: pointer to a function used in arithmetic [-Wpointer-arith]
   sum+=a[i];
           ^
/in/foo.cc:5:11: error: assignment of function 'int sum(int*, int, int)'
/in/foo.cc:5:11: error: cannot convert 'int (*)(int*, int, int)' to 'int(int*, int, int)' in assignment
/in/foo.cc:7:9: error: invalid conversion from 'int (*)(int*, int, int)' to 'int' [-fpermissive]
  return sum;
         ^~~