方法一: #include using namespace std; int main() { long long arr[10] = {9,99,999,9999,99999,999999,9999999,99999999,999999999,9999999999}; for(int i = 0; i < 10; i++){ sum += arr[i]; } cout << sum << endl; return 0; } 方法二: #include using namespace std; int main() { long long a = 9; long...