Help with a class. Any advice appreciated.

[Michael_Bray]

Hi,

I don't know where my program is going wrong, but I can't get it to compile. I have 3 files, dq.h, dq.cpp and dqtester.cpp

I have no problems with adding functions to the linked list once its done, I just need to class to compile so I can add functions to it. I have no idea where I am going wrong. If someone can point out where I have gone wrong I would appreciate it, I really need this to compile so I can start adding functions and making the queue work.

dq.h

#include <iostream>

struct node
{

  int item;
  node* next;

};  

class dqueue
{

  public:
    dqueue( );
    bool empty( );
  
  private:
    int size;
    node* front;

};
 

#include "dq.cpp"
#endif

dq.cpp

#include "dq.h"

dqueue::dqueue( )
{
  front = NULL;
  size = 0;
}

bool dqueue::empty()
{
  if (size == )
    return true;
  return false;
}

dqtester.cpp

#include <iostream.h>
#include "dq.h"

void main()
{

      cout<<"Yes!";
}

I am really bad with classes but I am trying to learn. I have been mucking around with this, rewriting it over and over again for hours. Its 2.30 am. If someone can point out where I have gone wrong I would appreciate it. I don't know if I am meant to declare the node struct in a different file then the .h or if I have a syntax error or logic error but I am pulling my hair out and I can't take it anymore

I know some of you guys are very good at C++ - If you can give me any advice about getting good at classes I would be grateful. I know they are important, I just can't get good at them no matter what I do. I guess I just need practise.

[riis]

in dqueue::empty():

  if (size == )
    return true;

Didn't you just forget to give the second variable for the comparision of "size"?

Another problem might be that you declared node as a structure. If you want to use that structure as a variable type, you need to declare "front" and "next" as "struct node* front" and "struct node* next". (The same goes for the "next" variable inside the structure.) Another option is to declare the structure as following:

typedef struct node_t
{

  int item;
  node* next;

} node;

This will declare node_t as a structure and with the typedef statement you create a new variable type node as struct node_t.

[CornedBee]

No riis, that goes only for C, in C++ his way is ok.

But the other thing should be right.

Look, Michael_Bray, you IDE (VC++ or Borland or whatever) should have a small output window at the bottom where compile errors are written to. Double-clicking such an error will take to directly to the line where the error occurred. Search in this line (and a few above and beyond) for the error. The compiler also outputs an error message. In your case it should be
error C2059: syntax error : ')'
assuming you use VC++.

What does that mean? That in the line the message points to:
if (size == )
the compiler encountered something it couldn't do anything with. In this case it was the ')'. ) is no expression that could be compared to something else, so ) is a syntax error here.

[Yonatan]

Also,

Originally posted by Michael_Bray

#include "dq.cpp"

You should never be #include'ing .c or .cpp files, only .h files.
As long as the .cpp file is a part of your project, it will be compiled.

[Michael_Bray]

Thanks for pointing that out. I feel like an idiot I spent hours on that, looking for some weird problem.

[riis]

Originally posted by CornedBee
No riis, that goes only for C, in C++ his way is ok.

Well, I guess I've learnt something more. The book from which I learnt C++ didn't mention it, probably because it went to dealing with classes almost immediately.