Compilare: user.cpp: In function ‘void Read()’: user.cpp:36:12: warning: unused variable ‘j’ [-Wunused-variable] int i, j; ^ user.cpp:38:34: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf( f, "%d%d\n", &N, &M ); ^ user.cpp:39:28: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets( a + 1, MAXN, f ); ^ user.cpp: In function ‘void Write()’: user.cpp:83:36: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf( f, "%d%d", &x, &y ); ^ 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* fgets(char*, int, FILE*)’, inlined from ‘void Read()’ at user.cpp:39:28: /usr/include/i386-linux-gnu/bits/stdio2.h:253:58: warning: call to ‘__fgets_chk_warn’ declared with attribute warning: fgets called with bigger size than length of destination buffer [enabled by default] return __fgets_chk_warn (__s, __bos (__s), __n, __stream); ^