You are returning a pointer to a stack memory location. That memory region is no longer valid once the function returns.

Also, instead of actually returning a pointer to the array, you are returning the first element in the array. The following code will return 1, not a pointer the array.

Use with AIint array[] {1, 2, 3, 4};
return *array

You probably only need to make minimal changes your code to get it to work.

Use with AIvoid** array = (void **) malloc(sizeof(void *) * array_size); 
...
return array;

Just make sure that you release the memory that memory used for array when you are finished with it.

Use with AIvoid **array = list_to_array(list);
// Use array
...
// Finished with array
free(array);

This is the error (as pointed out from Darkshadw and Jon Skeet)

Use with AIlistItem myList = new List<listItem>();

You are assigning the value of a List to a listItem.

Replace it with

Use with AIList<listItem> myList = new List<listItem>();

to create a list of listItem. Then

Use with AIlistItem[] myArray = myList.ToArray();

will work.

The following code works on arbitrary lists:

import ctypes
py_values = [1, 2, 3, 4]
arr = (ctypes.c_int * len(py_values))(*py_values)

Try using

MyClass[] myArray = list.ToArray();

Why don't you try doing:

myclass[] arr = data.ToArray();

Edit: To return the array so it's visible from VBA, you'd need to have your class as ComVisible.

[ComVisible(true)]
public class main
{
    public list<myclass> data  { get; set; }
}
[ComVisible(true)]
public class myclass
{
    public string variety { get; set; }
    public string ordertype { get; set; }
    public string producttype { get; set; }
}
[ComVisible(true)]
public myclass[] myclasses()
{
     myclass[] arr = data.ToArray();
     return arr;
}

@freeflow has a great reference link that you can use: https://analystcave.com/excel-use-c-sharp-in-excel-vba/

Since we believe you mean by dictionary, and by the ContentNumber, here is an example:

void Main()
{
    List<Word> Words = new List<UserQuery.Word> { new Word { CategoryNumber = 0, EnglishName = "WORD1" }, new Word { CategoryNumber = 1, EnglishName = "WORD2" }, new Word { CategoryNumber = 1, EnglishName = "WORD3" } };

    Dictionary<CategoryTypes, List<Word>> categoryWords = Words.GroupBy(word => word.CategoryNumber).ToDictionary(x => (CategoryTypes)x.Key, x => x.ToList());

    if (categoryWords.ContainsKey(CategoryTypes.Category2))
    {
        List<Word> words = categoryWords[CategoryTypes.Category2];

        for (int i = 0; i < words.Count; i++)
        {
            Console.WriteLine(words[i].EnglishName);
        }
    }
}

class Word
{
    public int CategoryNumber { get; set; }
    public string EnglishName { get; set; }
}

enum CategoryTypes
{
    Category1 = 0,
    Category2 = 1
}

You can then call the dictionary categoryWords by the type of enum, and then only have your list of words.