c++ returning a single value from a linked list

Question

I have the following code but it gives an error on the line - e = list.first();(towards the end of the code). It says that it cannot convert Node to char can someone tell me how to get return the first value from the linked list in the variable e.

Thanks for all the help:)

//
//  main.cpp
//  cprogram1
//

#include <iostream>

using namespace std;
class Node {
    char data;
    Node* next;

public:
    Node() {};
    void SetData(int aData) { data = aData; };
    void SetNext(Node* aNext) { next = aNext; };
    char Data() { return data; };
    Node* Next() { return next; };
};

// List class
class List {
    Node *head;
public:
    List() { head = NULL; };
    void Print();
    void Append(int data);
    void Delete(int data);
    Node * First() const;
};

/**
 * Print the contents of the list
 */
void List::Print() {

    // Temp pointer
    Node *tmp = head;

    // No nodes
    if ( tmp == NULL ) {
        cout << "EMPTY" << endl;
        return;
    }

    // One node in the list
    if ( tmp->Next() == NULL ) {
        cout << tmp->Data();
        cout << " --> ";
        cout << "NULL" << endl;
    }
    else {
        // Parse and print the list
        do {
            cout << tmp->Data();
            cout << " --> ";
            tmp = tmp->Next();
        }
        while ( tmp != NULL );

        cout << "NULL" << endl;
    }
}

/**
 * Append a node to the linked list
 */
void List::Append(int data) {

    // Create a new node
    Node* newNode = new Node();
    newNode->SetData(data);
    newNode->SetNext(NULL);

    // Create a temp pointer
    Node *tmp = head;

    if ( tmp != NULL ) {
        // Nodes already present in the list
        // Parse to end of list
        while ( tmp->Next() != NULL ) {
            tmp = tmp->Next();
        }

        // Point the last node to the new node
        tmp->SetNext(newNode);
    }
    else {
        // First node in the list
        head = newNode;
    }
}

/**
 * Delete a node from the list
 */
void List::Delete(int data) {

    // Create a temp pointer
    Node *tmp = head;

    // No nodes
    if ( tmp == NULL )
        return;

    // Last node of the list
    if ( tmp->Next() == NULL ) {
        delete tmp;
        head = NULL;
    }
    else {
        // Parse thru the nodes
        Node *prev;
        do {
            if ( tmp->Data() == data ) break;
            prev = tmp;
            tmp = tmp->Next();
        } while ( tmp != NULL );

        // Adjust the pointers
        prev->SetNext(tmp->Next());

        // Delete the current node
        delete tmp;

    }
}

Node * List::First() const {
    Node *tmp = head;
    return head;
}

int main ()
{
    char c;
    int t = 0;
    char e;
    List list;
    while(t==0)
    {
        cout << "Please enter your command";
        cin >> c;
        if(c=='c')
        {
            cout << "You will need to enter 6 letters, one after the other";
            cout << "Please enter the first letter";
            cin >> e;
            list.Append(e);
            cout << "Please enter the second letter";
            cin >> e;
            list.Append(e);
            cout << "Please enter the third letter";
            cin >> e;
            list.Append(e);
            cout << "Please enter the fourth letter";
            cin >> e;
            list.Append(e);
            cout << "Please enter the fifth letter";
            cin >> e;
            list.Append(e);
            cout << "Please enter the sixth letter";
            cin >> e;
            list.Append(e);
            list.Print();
            list.Delete('b');
            list.Print();
            e = list.First();


        }
    }
}

Gabriel L. · Accepted Answer · 2013-11-17 01:23:08Z

Lets take a look to your program : tested here :

#include <iostream>

using namespace std;

class Node {
   char data;
   Node* next;

public:
    Node() {};
    void SetData(int aData) { data = aData; };
    void SetNext(Node* aNext) { next = aNext; };
    char Data() { return data; };
    Node* Next() { return next; };
};

 // List class
 class List {
    Node *head;
 public:
    List() { head = NULL; };
    void Print();
    void Append(int data);
    void Delete(int data);
    Node * First() const;
  };

   /**
   * Print the contents of the list
   */
   void List::Print() {

    // Temp pointer
    Node *tmp = head;

   // No nodes
    if ( tmp == NULL ) {
        cout << "EMPTY" << endl;
    return;
  }

  // One node in the list
  if ( tmp->Next() == NULL ) {
    cout << tmp->Data();
    cout << " --> ";
    cout << "NULL" << endl;
  }
  else {
  // Parse and print the list
  do {
    cout << tmp->Data();
    cout << " --> ";
    tmp = tmp->Next();
  }
  while ( tmp != NULL );

  cout << "NULL" << endl;
  }
}

/**
 * Append a node to the linked list
 */
void List::Append(int data) {

    // Create a new node
    Node* newNode = new Node();
    newNode->SetData(data);
    newNode->SetNext(NULL);

    // Create a temp pointer
    Node *tmp = head;

    if ( tmp != NULL ) {
        // Nodes already present in the list
        // Parse to end of list
        while ( tmp->Next() != NULL ) {
            tmp = tmp->Next();
        }

        // Point the last node to the new node
        tmp->SetNext(newNode);
    }
    else {
        // First node in the list
        head = newNode;
    }
}

/**
 * Delete a node from the list
 */
 void List::Delete(int data) {

    // Create a temp pointer
    Node *tmp = head;

    // No nodes
    if ( tmp == NULL )
        return;

    // Last node of the list
    if ( tmp->Next() == NULL ) {
        delete tmp;
        head = NULL;
    }
    else {
        // Parse thru the nodes
        Node *prev;
        do {
            if ( tmp->Data() == data ) break;
            prev = tmp;
            tmp = tmp->Next();
        } while ( tmp != NULL );

        // Adjust the pointers
        prev->SetNext(tmp->Next());

        // Delete the current node
        delete tmp;

        }
 }

 Node * List::First() const {
    Node *tmp = head;
    return head;
}

int main ()
{
    char c;
    int t = 0;
    char e;
    List list;
    while(t==0)
    {
        cout << "Please enter your command";

        c = 'c';
        //cin >> c;
       if(c=='c')
    {
    cout << "You will need to enter 6 letters, one after the other";
    cout << "Please enter the first letter";

    list.Append('e');
    cout << "Please enter the second letter";
    //cin >> e;
    list.Append('a');
    cout << "Please enter the third letter";
    //cin >> e;
    list.Append('b');
    cout << "Please enter the fourth letter";
    //cin >> e;
    list.Append('f');
    cout << "Please enter the fifth letter";
    //cin >> e;
    list.Append('h');
    cout << "Please enter the sixth letter";
    //cin >> e;
    list.Append(e);
    list.Print();
    list.Delete('b');
    list.Print();
    e = list.First()->Data();
    t=1;
}
}

}

As you can see, e = list.First() return a pointer to a Node, not a char. You have implemented a function that return a char which is Data(). Thus, you should use e = list.First()->Data();.

Also, your loop is infinite because t is always 0. I just put t=1 to stop your loop and see the result. (if you use this code, don't forget to uncomment the cin and remove c = 'c')

Hope that helps you.

Bruce Dean · Accepted Answer · 2013-11-17 01:18:59Z

1

When I run your code I get the error:

main.cpp: error: assigning to 'char' from incompatible type 'Node *'
            e = list.First();
              ^ ~~~~~~~~~~~~

which I think explains it.

answered Nov 17, 2013 at 1:18

Bruce Dean

2,8082 gold badges21 silver badges31 bronze badges

Comments

fbafelipe · Accepted Answer · 2013-11-17 01:22:06Z

1

Try this:

e = list.First()->Data();

answered Nov 17, 2013 at 1:22

fbafelipe

4,9523 gold badges28 silver badges42 bronze badges

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