sortbooks.cpp: In function 'int main()':
sortbooks.cpp:29:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
29 | freopen ("task.inp", "r", stdin);
| ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
sortbooks.cpp:30:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
30 | freopen ("task.out", "w", stdout);
| ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
sortbooks.cpp:33:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
33 | freopen (task".inp", "r", stdin);
| ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
sortbooks.cpp:34:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
34 | freopen (task".out", "w", stdout);
| ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~