/in/foo.c: In function 'main':
/in/foo.c:53:11: error: incompatible type for argument 1 of 'power'
     power(result, x, n);
           ^~~~~~
/in/foo.c:26:6: note: expected 'BigInt * {aka struct <anonymous> *}' but argument is of type 'BigInt {aka struct <anonymous>}'
 void power(BigInt *result, int x, int n) {
      ^~~~~