Compilare: user.cpp: In constructor ‘state_machine::tree::tree()’: user.cpp:30:23: warning: converting to non-pointer type ‘int’ from NULL [-Wconversion-null] cnt_words = NULL; ^ user.cpp:32:26: warning: converting to non-pointer type ‘int’ from NULL [-Wconversion-null] cnt_children = NULL; ^ user.cpp:33:29: warning: converting to non-pointer type ‘int’ from NULL [-Wconversion-null] cnt_occurrences = NULL; ^ user.cpp: In member function ‘void state_machine::insert_word(state_machine::tree*, char*)’: user.cpp:45:24: warning: NULL used in arithmetic [-Wpointer-arith] if( *String == NULL ) { ^ user.cpp: In member function ‘int state_machine::delete_word(state_machine::tree*, char*)’: user.cpp:61:24: warning: NULL used in arithmetic [-Wpointer-arith] if( *String == NULL ) Node -> cnt_words --; else ^ user.cpp:67:53: warning: NULL used in arithmetic [-Wpointer-arith] if( Node != Root && Node -> cnt_children == NULL && Node -> cnt_words == NULL ) { ^ user.cpp:67:82: warning: NULL used in arithmetic [-Wpointer-arith] if( Node != Root && Node -> cnt_children == NULL && Node -> cnt_words == NULL ) { ^ user.cpp: In member function ‘int state_machine::count_word(state_machine::tree*, char*)’: user.cpp:77:24: warning: NULL used in arithmetic [-Wpointer-arith] if( *String == NULL ) ^ user.cpp: In member function ‘int state_machine::longest_prefix(state_machine::tree*, char*, int)’: user.cpp:88:24: warning: NULL used in arithmetic [-Wpointer-arith] if( *String == NULL ) ^ user.cpp: In member function ‘void state_machine::reset_machine(state_machine::tree*)’: user.cpp:99:33: warning: converting to non-pointer type ‘int’ from NULL [-Wconversion-null] Node -> cnt_occurrences = NULL; ^ user.cpp: In member function ‘void state_machine::build_occurrences(state_machine::tree*, char*)’: user.cpp:143:24: warning: NULL used in arithmetic [-Wpointer-arith] if( *String == NULL ) ^ user.cpp: In member function ‘void state_machine::build_partial_sum(state_machine::tree*)’: user.cpp:160:53: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < Node -> front_node.size(); i ++ ) { ^ user.cpp: In member function ‘int state_machine::count_occurrences(state_machine::tree*, char*)’: user.cpp:170:24: warning: NULL used in arithmetic [-Wpointer-arith] if( *String == NULL ) ^ user.cpp: In function ‘int main()’: user.cpp:237:33: warning: NULL used in arithmetic [-Wpointer-arith]