Compilare: user.cpp: In function ‘int main()’: user.cpp:20:14: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] a[l - 1] = NULL; ^ user.cpp:23:14: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] b[l - 1] = NULL; ^ user.cpp:18:27: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(a, 2000000, fin); ^ user.cpp:21:27: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(b, 2000000, fin); ^