Compilare: user.cpp: In function ‘void read()’: user.cpp:64:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n", &n, &m); ^ user.cpp:65:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] for (i = 1; i <= n; ++ i) ^ user.cpp:67:23: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] } ^ user.cpp: In function ‘void write()’: user.cpp:89:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] for (int i = l; i >= 1; -- i) ^ In file included from /usr/include/stdio.h:934:0, from /usr/include/c++/4.8/cstdio:42, from /usr/include/i386-linux-gnu/c++/4.8/bits/stdc++.h:46, from user.cpp:1: In function ‘char* gets(char*)’, inlined from ‘void read()’ at user.cpp:67:23: /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/ccZlcyAc.o: In function `read()': user.cpp:(.text+0xe5): warning: the `gets' function is dangerous and should not be used.