Compilare: user.cpp: In function ‘int main()’: user.cpp:39:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("base3.in","r",stdin); ^ user.cpp:40:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("base3.out","w",stdout); ^ user.cpp:43:23: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(mat[i]+1); ^ user.cpp:63:34: warning: array subscript is above array bounds [-Warray-bounds] int op[]={len[1],len[2],len[3],-len[1],-len[2],-len[3]}; ^ 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 ‘int main()’ at user.cpp:43:23: /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/ccd8Z1SH.o: In function `main': user.cpp:(.text.startup+0x51): warning: the `gets' function is dangerous and should not be used.