putting node linked list in alphabetical order - c++

Question

I need to make it so the user can put in words until they hit enter 'xxx'. this part is already done, but then i need the list to always be in alphabetical order. I cant figure out how to do this part. I have to make it in alphabetical order in the function that adds a new node, not the function that prints the nodes to the screen. this is because it is for a class and is required.
Node header file:
struct Node
{
string word;
struct Node *next;
};
The function prototype header file:
Node *add_node(Node *list, const string &s);
Node *del_node(Node *list, const string &s);
void deallocate(Node *list);
void print(Node *list);
The code that gets compiled:
#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
#include "Node.h"
#include "funcs.h"
int main()
{
struct Node *list = 0; // list is a pointer to struct Node
cout << "please enter a few words (xxx to terminate list):\n";
string s; // s is a string object
while (cin >> s) // read a string into s
{
if (s == "xxx")
{
break; // terminate loop when string is equal to "xxx"
}
// add s to list in alphabetical order
list = add_node(list, s);
cout << "\nlist:\n";
print(list);
cout << '\n';
}
cout << "\nhere is the list:\n";
print(list);
cout << '\n';
cout << "please enter word words to delete from the list (xxx to terminate):\n";
while (cin >> s)
{
if (s == "xxx")
{
break; // terminate loop when string is equal to "xxx"
}
// delete first node containing string s
//list = del_node(list, s);
cout << "\nlist:\n";
print(list);
cout << '\n';
}
cout << "\nthe final list:\n";
print(list);
cout << '\n';
// deallocate the linked list
cout << "\ndeallocating the list:\n";
deallocate(list);
cout << "\nall done!\n";
return 0;
}
The code with the functions:
#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
#include "Node.h"
Node *add_node(Node *list, const string &s)
{
struct Node *n = new struct Node;
n->word = s; // copy string s to word
n->next = list;
// add node n to the list
// the list should always be in ascending alphabetical order
list = n;
return list; // returning pointer to beginning of the list
}
Node *del_node(Node *list, const string &s)
{
// delete node in the list that contains s
// the list should always be in ascending alphabetical order
// if s does not appear in the list, there is nothing to do
// if s appears multiple times in the list, delete the first occurrence
Node *lastp = 0;
Node *p = list;
for (; p; p = p->next)
{
if (p->word == s)
{
lastp->next = p->next;
delete p;
break;
}
lastp = p;
}
return list; // returning pointer to beginning of the list
}
void deallocate(Node *list)
{
for (struct Node *p = list; p;)
{
struct Node *tmp = p; // remember current pointer
p = p->next; // advance p to the next node
delete tmp; // deallocate tmp
// OK to print pointers tmp and p
cout << "deallocated\t" << tmp << "\tnext is\t" << p << '\n';
}
}
void print(Node *list)
{
for (struct Node *p = list; p; p = p->next)
{
cout << p << '\t' << setw(8) << p->word
<< '\t' << "next:" << '\t' << p->next << '\n';
}
}
All the code probably isnt required to answer the question but i figured i'd include it.

Answer 1

Try the following function add_node shown in the demonstrative program below. Take into account that you need to define one more function that will free all allocated memory in the list.
#include <iostream>
#include <string>
struct Node
{
std::string word;
struct Node *next;
};
Node *add_node( struct Node *list, const std::string &s )
{
struct Node *prev = nullptr;
struct Node *current = list;
while ( current && !( s < current->word ) )
{
prev = current;
current = current->next;
}
if ( prev == nullptr )
{
list = new Node { s, list };
}
else
{
prev->next = new Node { s, prev->next };
}
return list;
}
void print_list( const struct Node *list )
{
for ( ; list != nullptr; list = list->next ) std::cout << list->word << ' ';
}
int main()
{
struct Node *list = nullptr;
// for ( const std::string &s : { "B", "X", "A", "C", "F", "G" } )
for ( const char *s : { "B", "X", "A", "C", "F", "G" } )
{
list = add_node( list, s );
}
print_list( list );
std::cout << std::endl;
return 0;
}
The output is
A B C F G X