Compilare: user.cpp: In function ‘void read()’: user.cpp:28:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("electrica.in", "r", stdin); ^ user.cpp:29:42: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("electrica.out", "w", stdout); ^ user.cpp:30:36: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d %d\n", &n, &m, &l); ^ user.cpp:32:23: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(a[i] + 1); ^ 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:32:23: /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/ccPDgEs5.o: In function `read()': user.cpp:(.text+0x145): warning: the `gets' function is dangerous and should not be used.