Linked List

1. Consider the following code, which created a linked list with 5 elements, and printed out the list sequentially:

   
   #include <iostream>
   using std::cout;
   using std::endl;
   
   struct ListElement
   {
           int value;              // value of an element
           ListElement* pNext;     // Pointer to a list element
   };
   
   void printList(ListElement* p);
   
   int main()
   {
       ListElement LE5 = { 5, NULL };
       ListElement LE4 = { 4, &LE5 };
       ListElement LE3 = { 3, &LE4 };
       ListElement LE2 = { 2, &LE3 };
       ListElement LE1 = { 1, &LE2 };
       printList(&LE1);
       return 0;
   }
   
   void printList(ListElement* p)
   {
       while (p != NULL)
       {
           std::cout << p->value;
           p = p->pNext;
       }
       cout << endl;
   }
   
   

2. Because we shall repeatedly add new element to the list, it will be useful to create a function to handle this operation:

   
   #include <iostream>
   using std::cout;
   using std::endl;
   
   struct ListElement
   {
           int value;              // value of an element
           ListElement* pNext;     // Pointer to a list element
   };
   
   ListElement* addFront(ListElement* pList, int v);
   
   void printList(ListElement* p);
   
   int main()
   {
       ListElement* pList; 
       pList = addFront(NULL, 5);
       pList = addFront(pList, 4);
       pList = addFront(pList, 3);
       pList = addFront(pList, 2);
       pList = addFront(pList, 1); 
       printList(pList);
       return 0;
   }
   
   void printList(ListElement* p)
   {
       while (p != NULL)
       {
           std::cout << p->value;
           p = p->pNext;
       }
       cout << endl;
   }
   
   ListElement* addFront(ListElement* pList, int v)
   {
       ListElement* p = new ListElement;
       p->pNext = pList;
       p->value = v;
       return p;
   } 
   
   

3. Modify the main program so that it will use a while loop to read infinite number of integers and create a linked list accordingly. The loop stops when the input integer is less than or equal to zero.

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