Inventory Linke list. How....

I wrote this program that I used the linked list to do the inventory. But I wnat to know how do I put in the following transactions: 1.Taking-in- updating the Quantity and price of the item(if it is in the list) or add it to the list if it is not.
2. Retail- sel x items for 105% of the price.
3. Order-form- List all the inventory.
4. Quit.

the following is the code:         I am using Borland C++5.01

#include      <iostream.h>
#include      <string.h>

// Necessary in Turbo C++
//enum bool      {false, true};
// The structure for the node - separately
// defined because it is self-referencing

typedef      struct      {
      char      itemcode[6];
      char      description[20];
      int      quantity;
        float      price;
}      item;
 
struct      node      {
      item            data;
      struct      node      *next;
} node;

// Pointer type to the node
typedef      struct node      *pnode;

class      list      {
public:
      list(void);
      list(item x);
      ~list(void);
      pnode      newnode(void);
      pnode      newnode(item x);
      void      addfront(item x);
      void      addrear(item x);
      void      insertafter(item x, pnode p);
      void      place(item x);
      bool      isxthere(char x[]);
      pnode      getptr(char x[]);
      void      removenode(char x[]);
      void      write(void);
private:
      pnode      lstart;
};

// list() -      The default constructor - Starts the list as empty
list::list(void)
{
      lstart = NULL;
}

// list() -      An initializing constructor that creates a node
//            and places in it the initial value
list::list(item x)
{
      lstart = new struct node;
      strcpy(lstart -> data.itemcode, x.itemcode);
      strcpy(lstart -> data.description, x.description);
      lstart -> data.quantity = x.quantity;
      lstart -> data.price = x.price;
      lstart -> next = NULL;
}

// ~list() -       The destructor
list::~list(void)
{
      pnode      p, q;

      // Go through the entire list, p points to the node because freed
      //      q points to the node after p
        if (lstart != NULL)
            for (p = lstart, q = p -> next;  q != NULL; p = q, q = p-> next)      
                  delete p;

    // When all is finished lstart is NULL
      lstart = NULL;
      delete q;
}

// newnode() -      Creates a new node with a zero as data
//            by default
pnode      list::newnode(void)
{
      pnode      p;

      p = new struct node;
      p -> data.itemcode[0] = '\0';
      p -> data.description[0] = '\0';
      p-> data.quantity = 0;
      p -> data.price = 0;
      return(p);      
}

// newnode() -      Creates a new node with the parameter x
//            as its value
pnode      list::newnode(item x)
{
      pnode      p;

      p = new struct node;
      p -> data = x;
      p -> next = NULL;
      return(p);      

}

// addfront() -      Inserts a new node containing x at
//            the front of the list
void      list::addfront(item x)
{
      pnode      p;

      p = newnode(x);
      p ->next = lstart;
      lstart = p;
}

// addrear() -       Inserts a new node containing x at
//            the rear of the list
void      list::addrear(item x)
{
      pnode      p, q;

      // Scan through the list to find the end
        // q points to the last node
      for (p = lstart, q= NULL; p != NULL; q = p, p = p -> next)      
            ;
      // Invariant - p must be NULL so we use it to hold a pointer
      // to the new node
      p = newnode(x);
      q -> next = p;
}

// insertafter() -      Insert value x in a new node to be inserted
//                  after p
void      list::insertafter(item x, pnode p)
{
      pnode       q;
      q = newnode(x);
      q -> next = p -> next;
      p -> next = q;
}

// isxthere() -      Is there a node on the list containing x?
bool      list::isxthere(char x[])
{
      pnode      p;

      if (lstart == NULL)
            return(false);

        // Scan through the list looking for x
      for (p = lstart; p != NULL && strcmp(p-> data.itemcode, x) != 0;
                  p = p -> next)
            ;
      // Invariant - either p contains x or we have gone through
        //      the entire list
      return((bool)(strcmp(p -> data.itemcode, x) == 0));
}

// getptr() - Get the pointer for the node containing x
pnode      list:: getptr(char x[])
{
      pnode      p;


        // Scan through the list looking for x
      for (p = lstart; p != NULL && strcmp(p-> data.itemcode, x) != 0;
                  p = p -> next)
            ;

      if (strcmp(p->data.itemcode, x) == 0)
              // p contains x
            return(p);
      else
            // We searched through the whole list and
                //      x wasn't there
            return(NULL);
}

// removenode() -      Remove the node containing x from the list
void      list::removenode(char x[])
{
      pnode      p, q;

        // Scan through the list - is x there?
      for (p = lstart, q = NULL;  p != NULL && strcmp(p-> data.itemcode, x) != 0;
                   p = p -> next)      
            q = p;

        // If so, remove it
      if (strcmp(p->data.itemcode, x) == 0)      {
            if (q == NULL)
                  // x is at the front
                  // Re-adjust the pointer to the
                        // front of the list
                  lstart = p -> next;
            else
                      // Splice it out of the list
                  q -> next = p -> next;

                // In either case, delete the node
            delete p;              
        }
}

// write() - Write the data contents of every node on the list
void      list::write(void)
{
      pnode      p;

      if (lstart == NULL)
            cout << "The list is empty" << endl;
        else
            for  (p = lstart; p != NULL; p = p -> next)
                  cout << p -> data.itemcode << '\t'
                        << p -> data.description << '\t'
                        << p -> data.quantity << '\t'
                        << p -> data.price << endl;
}

void      list::place(item x)
{
      pnode p, q;

      for (p = lstart, q = NULL;  p != NULL &&
                  strcmp(p -> data.itemcode, x.itemcode) <= 0;
                  q = p, p = p -> next)
            ;

      if (p == lstart)
            addfront(x);
      else
            insertafter(x, q);
}

int      main(void)
{
      list      mylist;
      item      stuff;

      mylist.write();
      strcpy(stuff.itemcode, "123");
      strcpy(stuff.description, "widget");
      stuff.price = 5.01;
      stuff.quantity = 5;
      mylist.place(stuff);
      mylist.write();

      return(0);
}

I used Retail price as:
Retail= Price + (Price * (10/100)).


Can anybody help me please.
Thanks!