Compilare: user.cpp: In function ‘void prime_no()’: user.cpp:15:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 2; prime[0] < n; ++ i) ^ user.cpp: In function ‘void read()’: user.cpp:27:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("per.in", "r", stdin); ^ user.cpp:28:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n", &n, &k); ^ user.cpp:29:16: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s + 1); ^ user.cpp: In function ‘void write()’: user.cpp:67:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("per.out", "w", stdout); ^ /tmp/cctnfJrs.o: In function `read()': user.cpp:(.text+0x10c): warning: the `gets' function is dangerous and should not be used.