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Linked Lists: Find length and check for empty list

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Linked Lists: Find length and check for empty list

 
0
  #1
Nov 11th, 2008
Hello..


This is what my program is suppose to do:

-find length of list
-check for empty list
-insert in back of list
-delete from front of list

I have everything done except finding the length of list and check for empty list.


I need help getting the length of my Linked list. I'm using a counter, but where do I place the counter in my program?

Also, I need help checking for empty list. There is no code in the book that shows me how to complete this task, so I don't even know how to check for it. Any help is appreciated...Thanks


I will post the 2 pieces of code that i'm working with and post the whole program below....



Here is my code:

C++ Syntax (Toggle Plain Text) 
  1. void createList(nodeType*& first, nodeType*& last);
  2. void printList(nodeType*& first);
  3. int listCount();
  4. bool emptyList();
  5. void insertBack(nodeType*& last);
  6. void deleteFront(nodeType*& first);
  7.  
  8. int main()
  9. {
  10.  
  11.     nodeType *first, *last;
  12.     int num;
  13.     int emptyList;
  14.     int count = 0;
  15.  
  16.     createList(first,last);
  17.     printList(first);
  18.  
  19.     if (emptyList(first))
  20.    cout<<"Empty list"<<endl;
  21.     else
  22.    cout<<"There are"<<listCount(first)<<" items in the linked list"<<endl;





C++ Syntax (Toggle Plain Text) 
  1. int listCount()
  2. {
  3.  
  4.   return count; 
  5.  
  6. }
  7.  
  8. bool emptyList()
  9. {
  10.  
  11.  
  12. }




THIS IS THE FULL CODE:



C++ Syntax (Toggle Plain Text) 
  1. #include <iostream>
  2.  
  3. using namespace std;
  4. struct nodeType
  5. {
  6.     int info;
  7.     nodeType *link;
  8. };
  9.  
  10. void createList(nodeType*& first, nodeType*& last);
  11. void printList(nodeType*& first);
  12. int listCount();
  13. bool emptyList();
  14. void insertBack(nodeType*& last);
  15. void deleteFront(nodeType*& first);
  16.  
  17. int main()
  18. {
  19.  
  20.     nodeType *first, *last;
  21.     int num;
  22.     int emptyList;
  23.     int count = 0;
  24.  
  25.     createList(first,last);
  26.     printList(first);
  27.  
  28.     if (emptyList(first))
  29.    cout<<"Empty list"<<endl;
  30.     else
  31.    cout<<"There are"<<listCount(first)<<" items in the linked list"<<endl;
  32.  
  33.  
  34.     insertBack(last);
  35.     printList(first);
  36.  
  37.     deleteFront(first);
  38.     printList(first);
  39.  
  40.   system("PAUSE");
  41.    return 0;
  42. }
  43.  
  44. void createList(nodeType*& first, nodeType*& last)
  45. {
  46.     int number;
  47.     nodeType *newNode;
  48.  
  49.     first = NULL;
  50.     last = NULL;
  51.  
  52.     cout<<"Enter an integer (-999 to stop): ";
  53.     cin>>number;
  54.     cout<<endl;
  55.  
  56.      while (number != -999)
  57.      {
  58.          newNode = new nodeType; // create new node
  59.          newNode->info = number;
  60.          newNode->link = NULL;
  61.  
  62.          if (first == NULL)
  63.          {
  64.             first = newNode;
  65.             last = newNode;
  66.          }
  67.          else
  68.          {
  69.            last->link = newNode;
  70.            last = newNode;
  71.          }
  72.          cout<<"Enter an integer (-999 to stop): ";
  73.          cin>>number;
  74.          cout<<endl;
  75.      }
  76.  
  77. }
  78.  
  79. void printList(nodeType*& first)
  80. {
  81.  
  82.     cout<<"Inside printList...printing linked list...\n"<<endl;
  83.         nodeType *current;
  84.         current = new nodeType;
  85.         current = first;    
  86.         while (current != NULL)
  87.         {
  88.           cout << current->info<<endl;
  89.           current = current->link;
  90.           count++;
  91.         }
  92. }  
  93.  
  94.  void insertBack(nodeType*& last)
  95. {
  96.  
  97.   int num;
  98.   nodeType *first,*newNode;
  99.  
  100.  
  101.   cout<<"There are 3 items in the linked list."<<endl;
  102.   cout<<"Enter a number to add to the END of the list: "<<endl;
  103.   cin>>num;
  104.  
  105.  
  106.          newNode = new nodeType;
  107.          newNode->info = num;
  108.          newNode->link = NULL;
  109.  
  110.          if (first == NULL)
  111.          {
  112.            first = newNode;
  113.            last = newNode;
  114.  
  115.          }
  116.          else
  117.          {
  118.            last->link = newNode;
  119.            last = newNode;
  120.          }
  121.  
  122. }
  123.  
  124. void deleteFront(nodeType*& first)
  125. {
  126.  
  127.   nodeType *last,*current,*trailcurrent;
  128.   bool found;
  129.  
  130.  
  131.   cout<<endl;
  132.   cout<<"Inside deleteFront...removing item from front of list..."<<endl;
  133.   cout<<endl;
  134.  
  135.          if (first->info == 1)
  136.          {
  137.            current = first;
  138.            first = first->link;
  139.          }
  140.          if (first == NULL)
  141.          {
  142.             last = NULL;
  143.  
  144.             delete current;
  145.          }
  146.          else
  147.          {
  148.          found = false;
  149.          trailcurrent = first;
  150.  
  151.          current = first->link;
  152.          }
  153.  
  154.  
  155.  
  156. }
  157.  
  158. int listCount()
  159. {
  160.  
  161.   return count; 
  162.  
  163. }
  164.  
  165. bool emptyList()
  166. {
  167.  
  168.  
  169. }
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Re: Linked Lists: Find length and check for empty list

 
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  #2
Nov 11th, 2008
Well, you obvioulsy need to increment counter each time you add a node, and decrement it each time you remove a node. It's really not hard, just put it in insert, delete, and create list.

For checking if list is empty... simply check if first==NULL.

But don't you need some wrapper class around everything? This way it's meaningless to write empty() function
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Re: Linked Lists: Find length and check for empty list

 
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  #3
Nov 11th, 2008
If unlucky user accidentally types a wrong char your program comes to loop forever because subsequent cin inputs do nothing until cin.clear() call.
Always check input result, for example:
C++ Syntax (Toggle Plain Text) 
  1. if (cin >> number) {
  2.    // that's ok
  3. } else {
  4.    // eof or not-a-number
  5.    // Recovery? It's the other story...
  6. }
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