Compilare: user.cpp: In function ‘int main()’: user.cpp:63:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("substr.in", "r", stdin); ^ user.cpp:64:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("substr.out", "w", stdout); ^ user.cpp:66:36: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d %d\n", &N, &K), sa.N = N; ^ user.cpp:67:15: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets (sir + 1); ^ /tmp/cc0Djb1p.o: In function `main': user.cpp:(.text.startup+0x7c): warning: the `gets' function is dangerous and should not be used.