Compilare: user.cpp: In function ‘int main()’: user.cpp:69:30: 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:70:25: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(c+1,1000005,f); ^ user.cpp:97:34: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f,"%c %c\n",&a,&b); ^ 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 ‘int main()’ at user.cpp:70:25: /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); ^