Compilare: user.cpp: In function ‘int ok(int, int)’: user.cpp:25:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < V[x].size(); ++ i) ^ user.cpp: In function ‘void read()’: user.cpp:33:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("abc2.in", "r", stdin); ^ user.cpp:34:12: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s); ^ user.cpp:38:20: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(a[nr]); ^ user.cpp: In function ‘void write()’: user.cpp:74:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("abc2.out", "w", stdout); ^ In file included from /usr/include/stdio.h:934:0, from /usr/include/c++/4.8/cstdio:42, from user.cpp:1: In function ‘char* gets(char*)’, inlined from ‘void read()’ at user.cpp:38:20: /usr/include/i386-linux-gnu/bits/stdio2.h:230:28: warning: call to ‘__gets_warn’ declared with attribute warning: please use fgets or getline instead, gets can't specify buffer size [enabled by default] return __gets_warn (__str); ^ /tmp/cct1EBJM.o: In function `read()': user.cpp:(.text+0x38b): warning: the `gets' function is dangerous and should not be used. user.cpp:(.text+0x361): warning: the `gets' function is dangerous and should not be used.