Compilare: user.cpp:5:0: warning: "NULL" redefined #define NULL 0 In file included from /usr/include/string.h:32:0, from /usr/include/c++/6/cstring:42, from user.cpp:2: /usr/lib/gcc/x86_64-linux-gnu/6/include/stddef.h:403:0: note: this is the location of the previous definition #define NULL __null user.cpp: In function ‘int main()’: user.cpp:15:29: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(fin, "%d%d", &N, &K); ^ user.cpp:17:26: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(WT, 10000001, fin); ^