Struct pointer initialization

Hello everyone,
I wrote a piece of code here, which actually works, but I was told to initialize the data structure that holds the data to be filtered and I dont really understand how to do this.
As you can see

Quote:

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double* Values; // holds the data to be filtered

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The pointer Values will be used to create a dynamic array, but first I was told to initialize it . So, how do I initialize it?
I have a function

Quote:

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void EnterData(TheData& DataIn)
{
// initialize the data structure that holds the data to be filtered, including getting
// the number of data values from the user

cout << "Please enter the number of data values to be filtered:" << endl;
cin >> DataIn.Length;
cout << endl;

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So, I was trying to write something like DataIn.Values = NULL to initialize the structure where data will be held, but it doesnt really work.
Thank you for any help.
Here is a full code.

Code:

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#include <iostream>
using namespace std;

struct TheData
{
  double* Values;  // holds the data to be filtered
  unsigned long Length;  // number of data values
  bool Valid;  // true if the data values have been Valid by the user
};

void EnterData(TheData&);


int main()
{
        int a;
        TheData OriginalData = {0,0,false};
        EnterData(OriginalData);
        cout << endl;
        //cout << OriginalData.Length;
        cin >> a;
        delete [] OriginalData.Values;
       
}
// Allow the user to enter the data to be filtered
// Arguments:
//  (1) the structure containing the input data
// Returns: nothing
//
void EnterData(TheData& DataIn)
{ 
        // initialize the data structure that holds the data to be filtered, including getting
        // the number of data values from the user

        cout << "Please enter the number of data values to be filtered:" << endl;
        cin >> DataIn.Length;
        cout << endl;

        // allocate memory to the data
        DataIn.Values = new(double[DataIn.Length]);

        // obtain all of the data values
        cout << "Please enter the data values to be filtered:" << endl;
        for (unsigned int i=0; i<DataIn.Length; i++)
                {
                        cout << "Please enter value #" << i+1 << ": ";
                        cin >> DataIn.Values[i];
                }
        DataIn.Valid = true;
        cout << "All the values were saved successfully.";
}

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Quote:

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Originally Posted by pe4enka

The pointer Values will be used to create a dynamic array, but first I was told to initialize it . So, how do I initialize it?

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You did it correctly on this line, by initialising the member variable to be a null pointer:

Code:

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TheData OriginalData = {0,0,false};

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By the way, it is more common to write this:

Code:

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DataIn.Values = new(double[DataIn.Length]);

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as:

Code:

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DataIn.Values = new double[DataIn.Length];

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Yes, but the task tells to initialize Values again in the function. I dont really understand why and how as well as what for. but this is the task given. I need to do it in the place, where I colored with green So, is there any way? because if I say, create another pointer like
double **testpointer and write
testpointer = &DataIn.Values to check the address of DataIn.Values, then testpointer will point to some memory location, where DataIn.Values is being kept and this address appears to be not zero... How do I make this pointer DataIn.Values to point nowhere, until I allocate memory for DataIn.Values using new?

Quote:

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Originally Posted by pe4enka

Yes, but the task tells to initialize Values again in the function.

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That is impossible. By definition, you can only initialise once. You could simply fail to initialise OriginalData in the main function and then assign an initial value to OriginalData in the EnterData function, yet even then technically that would not be initialisation.

Quote:

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Originally Posted by pe4enka

because if I say, create another pointer like
double **testpointer and write
testpointer = &DataIn.Values to check the address of DataIn.Values, then testpointer will point to some memory location, where DataIn.Values is being kept and this address appears to be not zero...

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That is expected. The pointer itself has an address, regardless of whether it is a null pointer or if it points somewhere.

Quote:

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Originally Posted by pe4enka

How do I make this pointer DataIn.Values to point nowhere, until I allocate memory for DataIn.Values using new?

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You already did that correctly by initialising it to be a null pointer.

Thank you for your help. I guess I will leave just DataIn.Values = NULL, because I can't read my lectruer's mind lol