Compilare: main.cpp: In function 'int main()': main.cpp:49:13: warning: converting to non-pointer type 'char' from NULL [-Wconversion-null] c1[lg1]=NULL; ^~~~ main.cpp:52:13: warning: converting to non-pointer type 'char' from NULL [-Wconversion-null] c2[lg2]=NULL; ^~~~ main.cpp:46:20: warning: ignoring return value of 'char* fgets(char*, int, FILE*)', declared with attribute warn_unused_result [-Wunused-result] fgets(c1+1,N,f); ^ main.cpp:47:20: warning: ignoring return value of 'char* fgets(char*, int, FILE*)', declared with attribute warn_unused_result [-Wunused-result] fgets(c2+1,N,f); ^ In file included from /usr/include/stdio.h:936:0, from /usr/include/c++/6/cstdio:42, from main.cpp:1: In function 'char* fgets(char*, int, FILE*)', inlined from 'int main()' at main.cpp:46:20: /usr/include/x86_64-linux-gnu/bits/stdio2.h:261:58: warning: call to '__fgets_chk_warn' declared with attribute warning: fgets called with bigger size than length of destination buffer return __fgets_chk_warn (__s, __bos (__s), __n, __stream); ^ In function 'char* fgets(char*, int, FILE*)', inlined from 'int main()' at main.cpp:47:20: /usr/include/x86_64-linux-gnu/bits/stdio2.h:261:58: warning: call to '__fgets_chk_warn' declared with attribute warning: fgets called with bigger size than length of destination buffer return __fgets_chk_warn (__s, __bos (__s), __n, __stream); ^