"Read numbers until -1 is entered, then stop" — best loop pattern
- A
do { input = read(); } while (input != -1);
- B
for (int i = 0; i < n; i++)
- Ccheck_circle
Both A and C are reasonable
- D
while (input != -1) { ...; input = read(); }
Explanation
Either pattern (priming-read while or do-while) handles sentinel.