Compilare: user.cpp: In function ‘int main()’: user.cpp:172:13: warning: NULL used in arithmetic [-Wpointer-arith] if(up[a]==NULL) ^ user.cpp:164:23: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(in,"%d",&n); ^ user.cpp:170:31: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(in,"%d%d%d",&a,&b,&c); ^