How can I use a search function on a dynamic array?

Question

I'm trying to use a linear search function on a dynamic array I created but then the teaching assistant for my computer science class told us that most search functions use const arrays.

Is there any way I can edit my dynamic array to become contant? Or is it also possible to make a search function that uses a dynamic array (and would not give errors?). I'll give a brief insight into my code:

I dynamically create an array using the rows I read in from a file and then dynamically allocate each row to an array of columns.

char ** domain[] = new char * [rows];

for(int i = 0; i < rows; i++)
{
    *domain = new char[columns];  
    domain++;  
}

The type of function that we were taught for searching is:``

char searchArray( const char list[], char letter, int maxSize)
{
    >code goes here  
}

Is there any other method of using a search function that takes in dynamic multidimensional arrays?

In response to the comments, I can't use vectors. This is an assignment for us to use normal arrays. I haven't been taught how to to use vectors yet.

Answer 1

In the line

char ** domain[] = new char * [rows];

char ** domain[] tries to make an array of char **. If the compiler didn't complain about not having a valid array size in the [] and you would have a 3D structure. You want just plain old char ** for a 2D structure, so

char ** domain = new char * [rows];

The loop filling out the inner dimension is correct except it loses track of the starting point of domain

for(int i = 0; i < rows; i++)
{
    *domain = new char[columns];  
    domain++;  
} 

Should be something like

char ** temp = domain;

for(int i = 0; i < rows; i++)
{
    *temp = new char[columns];
    temp++;
}

To preserve the starting point, but for this case array notation is probably the smarter and easier-to-read option.

for(int i = 0; i < rows; i++)
{
    domain[i] = new char[columns];
}

On to searchArray. It needs to know it's getting two dimensions, (const char **) and that there are two max sizes (maxRow and maxColumn). It will look something like

char searchArray(const char ** list, 
                 char letter, 
                 int maxRow, 
                 int maxColumn)
{
    >code goes here  
}

Code goes here is your problem, but will probably be two nested for loops iterating to maxRow and maxColumn and returning when letter is found.

But... Why return a char? Returning the location in the array is much more useful. We could use std::pair, but if std::vector is off limits, pair probably is as well. Consider something like the following instead:

struct coord
{
    int row;
    int column;
};

coord searchArray(const char ** list, 
                  char letter, 
                  int maxRow, 
                  int maxColumn)
{
    coord location;
    >code goes here
    return location;
}

If the item is not found, set row and column to something impossible to get like -1 so you can easily test for the not found case.

Stop here unless you want to <expletive deleted> with your teacher's brain.

The above doesn't build a 2D array. You can't get a dynamically allocated 2D array in C++. What you have is an array of arrays. There are a couple downsides to this, look at all the work that goes into stitching one together and computers love it when things go in straight lines. Array of arrays doesn't. Every different allocation can be somewhere completely different in memory forcing the program to hop around, waiting on and loading different chunks of memory. Sometimes The program will spend more time sitting around waiting for stuff to be found and loaded than it'll spend doing the actual work. This sucks.

The solution is to make a 1D array and make it look like a 2D array. Here's an example of that from the C++ FAQ

You'll learn a lot of neat stuff from following this example, not the least of which being RAII and the Rule of Three, two concepts without which you cannot write non-trivial high quality C++ code.