trouble initializing constructor

Code:

---


  class List
{

  public:
    List(const int* arr, int sz);
              //initializes list object by copying the data from the array arr (of size sz) into it


    int HowMany(int val); //returns the number of times the value val appears in the list


    void PrintSquares();  //prints squares of data elements in list, separated by commas


  private:
    int data[100]; //list of up to 100 numbers
    int size; //number of values currently stored

};

---

This is my header file. The following code now is the definition file. I'm supposed to initialize the constructor with a constant int pointer and that is the part that is giving me the trouble. I'm not so sure if i defined my other functions correctly. But if anyone can give me a heads up on how to go about solving the constructor problem and analyzing if I did the other functions right, I would really appreciate it. Thank you.

Code:

---

#include <iostream>
#include "list2.h"
using namespace std;


 List::List(const int* arr, int sz)
{
              //initializes list object by copying the data from the
              //array arr (of size sz) into it

 
 arr[data];// this part trips me out, I also tried this
  size=sz;

}

int List:: HowMany(int val) //returns the number of times the value
                                //val appears in the list
{
    int v=0;
    for(int i=0; i<size; i++)

 if (data[i]==val)
        v++;
 
      return v;
}

 
 
void List:: PrintSquares()  //prints squares of data elements in list,
                                //separated by commas
{
 for(int i=0; i<size; i++)
 {
  cout<<data[i]*data[i];

    for (int j=0;j<data[i];j++)
  cout<<',';

 cout<<endl;
 }
   
}

---

Hmmm K. Put the code tags but it didn't print out in a nice box, why???

Use the brackets, [ and ], instead of < and > for your code tags...

ahh thanks Spoon.

Code:

---

arr[data];    //this is bad
  size=sz;

---

You want to dynamicly create arr based on the value of sz. You also want to keep track of that with size, so you've got that part aokay.

Hmmm, you mean something like this?

size=sz;
arr= new int [size];


I'm a bit confused. I'm just now starting to learn about dynamic allocation. It compiles fine but i'm not sure if i'm on the right track. Thanks for your help.

I'm not entirely sure what the goal here is. Are you trying to make some sort of linked list? If you are, then you don't want to just dynamically allocate an array.

Is this an assignment for a class or an excercise out of book? Maybe you could clarify what you want to accomplish.

I just need to initialize list object by copying the data from the array arr (of size sz) into it. I'm stuck on that part.

This isn't for an assignment.

>I just need to initialize list object by copying the data from the array arr (of size sz) into it.

Code:

---

#include <stdexcept>

List::List(const int* arr, int sz)
{
  if (sz >= 100) {
    throw std::out_of_range("sz too large");
  }
  for (int i = 0; i < sz; i++) {
    data[i] = arr[i];
  }
}

---

Thank you all for your help on my constructor problem, I really appreciate it.

Just one more question about this problem. For my PrintSquares() function. To print out commas in between the integers but not after the last comma, is my for loop laid out correctly? should I replace the i<data[i] condition with i<size? I'm leaning towards the first one but I'm not too sure.

Code:

---

  for(int i=0; i<size; i++)
    {
      cout<<data[i]*data[i];   
 
      for (int j=0;j<data[i];j++) 
      cout<<',';
    }

---

You guys rule. Thanks for helping out a programming novice.

You either need to treat the first item specially or the last item specially. To do it by focusing on the first item, you print the item outside of the loop and then start with leading commas:

Code:

---

#include <iostream>

using namespace std;

int
main()
{
  int i = 0;

  cout<< i;
  for (i = 1; i < 10; i++) {
    cout<<", "<< i;
  }
  cout<<endl;
}

---

To focus on the last item, you need to test for whether you're at the end or not:

Code:

---

#include <iostream>

using namespace std;

int
main()
{
  int i;

  for (i = 0; i < 10; i++) {
    cout<< i;
    if (i != 9) {
      cout<<", ";
    }
  }
  cout<<endl;
}

---

Those examples should be easy to translate into what you need done. :)

Wow, thanks a lot. Makes sense. Thank you very much and everyone else to for helping me out. I really appreciate it. :cool: