/* listprog.cpp - Demo program to illustrate linked lists, uses a struct.

   Sample Run:

      This program finds sum or product of a variable number
      of integers. Enter as many integers > 0 as you would like
      followed by the value -1.

      The numbers are: 3 5 7 9 -1

      Just entered Fcn. displayList... 9 7 5 3

      Please select the number of one of these options:
         1. Sum the numbers in the list
         2. Multiply the numbers in the list
         3. Exit the program.
      Your choice: 1
      Answer is: 24




 */


#include <iostream>
#include <cstdlib>

using namespace std;

struct Node {
   int data;
   Node *nextPtr;
};


void displayList( Node *head)
{
   Node *tempPtr = head;  // Used to traverse list without destroying head
   cout << "\n List contains: ";
   while( tempPtr != NULL) {
      cout << tempPtr->data << " ";
      tempPtr = tempPtr->nextPtr;
   }
   cout << "\n\n";
}

long processNumbers( Node *head)
{
   Node *tempPtr = head;
   long result = 0;

   while (tempPtr != NULL) {
	    result += tempPtr->data;
       tempPtr = tempPtr->nextPtr; 	// Advance to next list member 
   }

   return result;
}


// First figure out the rest of the program before attempting to understand
// how reversing the list works.
Node *reversing( Node *head)
{
	Node *tempPtr;

	if (head->nextPtr == NULL)  {
		return head;
	}
	else {	// head->nextPtr != NULL 		
		tempPtr = reversing( head->nextPtr);
		head->nextPtr->nextPtr = head;	// reverse link 
		return tempPtr;
	}			
}


main()
{
   int number = 0;      // Used to store numbers read in 
   Node *head = NULL;   // head of linked list 
   Node *tempPtr;       // Temporary node pointer used in reversing list
   int menuChoice;      // Menu choice 

   cout << "This program finds sum or product of a variable number \n";
   cout << "  of integers. Enter as many integers > 0 as you would like \n";
   cout << "  followed by the value -1.\n\n";
   cout << "The numbers are: ";

   while ( number != -1) {
		cin >> number;
		if (number != -1) {
			tempPtr = new Node;
			// Insert at head of list 
			tempPtr->data = number;
			tempPtr->nextPtr = head;
			head = tempPtr;
		}
   }

   displayList( head);

   while (true)
     {
   cout << "Please select the number of one of these options: \n";
   cout << "   1. Sum the numbers in the list\n";
   cout << "   2. Reverse the list.\n";
   cout << "   3. Exit the program.\n";
   cout << "Your choice: ";
   cin >> menuChoice;

   switch ( menuChoice) {
      case 1:  // Sum numbers in list
               cout << "Answer is: " << processNumbers( head) << "\n";
               break;

      case 2:  // Reverse the list   
               cout << "Before reversing, the list looks like: ";
               displayList( head);

               tempPtr = head;            // keep track of original list head
               head = reversing( head);   // Reverse list
               tempPtr->nextPtr = NULL;   // set old head node pointer to point to NULL

               cout << "AFTER reversing, the list looks like: ";
               displayList( head);
               break;

      case 3:  // Exit the program
               exit( 0);
               break;
   }

   // pause output display
   
   

     }

   return 0;
}