How to set up explicit value constructor with linked list?

Question

For a project, im trying to set up a linked list object so that it can be initialized with an explicit value constructor. I want it to look like this:

WORD you("you");//where the object you's linked list now contains y o u;

but when I print out the object you, all i see is this symbol "=" and when I print out the length of you, I get -858993459

Here is my explicit value constructor, can someone tell me what I am doing wrong?

WORD::WORD(string s)
{
front = 0;
int i = 0;
int len = s.length();

if(front == 0)
{   
    front = new alpha_numeric;
    alpha_numeric *p = front;

    while(s[i] <= len)
    {
        p -> symbol = s[i];
        p -> next = new alpha_numeric;
        p = p -> next;
        p -> symbol = s[i++];
    }
    p -> next = 0;
}
}

Here is the class declaration file if it helps

#include <iostream>
#include <string>

using namespace std;
#pragma once

class alpha_numeric //node
{
public:
char symbol; //data in node
alpha_numeric *next;//points to next node
};

class WORD
{
public:
WORD(); //front of list initially set to Null
WORD(const WORD& other);
WORD(string s); //***EXPLICIT VALUE CONSTRUCTOR
bool IsEmpty(); //done
int Length();
void Add(char); //done
//void Insert(WORD bword, int position);
//void operator=(char *s);

friend ostream & operator<<(ostream & out, const WORD& w);//done

private:
alpha_numeric *front; //points to the front node of a list
int length;
};

Answer 1

You never set length, so that's why it's garbage. As luthien256 ahd LihO pointed out, your while loop is also wrong, and the if (front == 0) test makes no sense.

Finally, the p -> symbol = s[i++]; is not needed. Just increment i.

Try this:

class alpha_numeric //node
{
public:
char symbol; //data in node
alpha_numeric *next;//points to next node
};

class WORD
{
public:
WORD(); //front of list initially set to Null
WORD(const WORD& other);
WORD(string s); //***EXPLICIT VALUE CONSTRUCTOR
bool IsEmpty(); //done
int Length() { return length; }
alpha_numeric *Front() { return front; }
void Add(char); //done
//void Insert(WORD bword, int position);
//void operator=(char *s);

friend ostream & operator<<(ostream & out, const WORD& w);//done

private:
alpha_numeric *front; //points to the front node of a list
int length;
};

WORD::WORD(string s)
{
  front = 0;
  int i = 0;
  int len = s.length();
  length = len;
  if (length == 0) {
    front = NULL;
    return;
  }
  front = new alpha_numeric;
  alpha_numeric *p = front;

  while(i < len)
  {
      p -> symbol = s[i];
      if (i != len - 1) {
        p -> next = new alpha_numeric;
        p = p -> next;
      }
      else
        p -> next = NULL;
      ++i;
  }
}


int main() {
  WORD you("you");
  alpha_numeric* front = you.Front();
  while(front != NULL) {
    cout<<(front->symbol)<<endl;
    front = front->next;
  }
  cout<<you.Length()<<endl;
  return 0;
}

Answer 2

You have std::string s and int i initialized to 0. Then you have int len initialized to s.length(); and you want to iterate through this string:

while(s[i] <= len) <----------------- THIS IS WRONG
{
    ...
    p -> symbol = s[i++];
}

Also note, that complexity of std::basic_string::length() is O(1). There is no point of using temporary variable len. You are also doing a lot of redundant things like assigning 0 to front and then checking if (front == 0). It could look like this:

WORD::WORD(std::string s)
{
    length = s.length();
    if (length == 0)
    {
        front = NULL
        return;
    }

    front = new alpha_numeric;
    alpha_numeric *p = front;

    int i = 0;
    while(i < length - 1)
    {
        p->symbol = s[i++];
        p->next = new alpha_numeric;
        p = p->next;
    }
    p->symbol = s[i];
    p->next = NULL;
}

Answer 3

It's unlikely your while loop is executing. I believe:

while(s[i] <= len)

should be

while(i < len)

Answer 4

try this:

WORD::WORD(string s)
{
  int i;
  int len = s.length();

  front = new alpha_numeric;
  alpha_numeric *p = front;

  for(i = 0; i < len; i++)
  {
        p -> symbol = s[i];
        p -> next = (i == len - 1) ? 0 : new alpha_numeric;
        p = p -> next;
  }
}