Question

The problem appears with the insert function that I wrote.

3 conditions must work, I tested b/w 1 and 2, b/w 2 and 3 and as last element, they worked.

---

EDIT;
It was my own problem. I did not realize I put MAXINPUT = 3 (instead of 4). I do appreciate all the efforts to help me becoming a better programmer, using more advance and more concise features of C++.

Basically, the problem has been solved.

---

Efficiency is not my concern here (not yet). Please guide me through this debug process.

Thank you very much.

#include<iostream>
#include<string>
   using namespace std;

    struct List    // we create a structure called List
   {
      string name;  
      string tele;
      List *nextAddr;
   };

   void populate(List *);
   void display(List *);
   void insert(List *);

    int main()
   {
      const int MAXINPUT = 3;
      char ans;  

      List * data, * current, * point;  // create two pointers
      data = new List;
      current = data;

      for (int i = 0; i < (MAXINPUT - 1); i++)
      {
         populate(current);
         current->nextAddr = new List;
         current = current->nextAddr;
      }

   // last record we want to do it sepeartely

      populate(current);
      current->nextAddr = NULL;
      cout << "The current list consists of the following data records: " << endl;
      display(data);

   // now ask whether user wants to insert new record or not

      cout << "Do you want to add a new record (Y/N)?";

      cin  >> ans;

      if (ans == 'Y' || ans == 'y')
      {
     /* 

   To insert b/w first and second, use point as parameter
   between second and third uses point->nextAddr
   between third and fourth uses point->nextAddr->nextAddr
   and insert as last element, uses current instead 

   */       
   point = data;
   insert(());  
         display(data);
      }

      return 0;  
   }


    void populate(List *data)
   {
      cout << "Enter a name: ";
      cin >> data->name;
      cout << "Enter a phone number: ";
      cin >> data->tele;

      return;
   }

    void display(List *content)
   {
      while (content != NULL)
      {
         cout << content->name << "     " << content->tele;
         content = content->nextAddr;
         cout << endl; // we skip to next line
      }

      return;
   }

    void insert(List *last)
   {
      List * temp = last->nextAddr; //save the next address to temp
  last->nextAddr = new List; // now modify the address pointed to new allocation
      last = last->nextAddr; 
      populate(last);
      last->nextAddr = temp; // now link all three together, eg 1-NEW-2

      return;
   }

Answer 1

Your code works fine on my machine (once the insert(()) statement is “filled in” properly as explained in the code comment). The insertion works in all positions.

---

Something else, though: I initially had a look at your insert function. I thought I’d give you a hint on how to make it a little shorter and easier to understand what’s going on:

void insert(List *last)
{
    // create a new item and populate it:
    List* new_item = new List;
    populate(new_item);

    // insert it between 'last' and the item succeeding 'last':
    new_item->nextAddr = last->nextAddr;
    last->nextAddr = new_item;
}

This would be preferable because it first creates a new, separate item, prepare it for insertion, and only then, when this has worked successfully, will the function “mess” with the linked list. That is, the linked list is not affected except in the very last statement, making your function “safer”. Contrast this with your version of insert, where you mix code for constructing the new item with the actual insertion. If something goes wrong inside this function, chances are far higher that the linked list is messed up, too.

(What’s still missing btw. is a initial check whether the passed argument last is actually valid, ie. not a null pointer.)

---

P.S.: Of course you could just use a standard C++ std::list container instead of building your own linked list, but seeing that you tagged your question beginner, I assume you want to learn how it actually works.