/in/foo.cc: In function 'void chaifen(long long unsigned int)':
/in/foo.cc:8:6: warning: unused variable 'flag' [-Wunused-variable]
  int flag = 0;
      ^~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:85:16: error: 'system' was not declared in this scope
  system("pause");
                ^