Recursion, function, 2D array?

[ihatestarch]

What would a recursive function (not from a class) that puts some kind of element (like an integer) into a 2D array look like?

I noticed a 2D array seems to be a bit different from a regular array in a function.

Is the first bracket always empty and the second bracket hold the size?

void Array(int array[][10])

How can you change the value in the different rows and columns recursively? Or even how can you manipulate the rows and columns recursively? I feel as if I NEED the for loop. I couldn't find a model example of this in my book.

[vmanes]

Ouch - I'm getting a headache just thinking about a recursive 2D function - but it is a technique used in maze running problems. Your main concern is determining your base case and determining in what manner you will modify the parameters in the recursive call.

Concerning the array parameter, yes, you leave the highest order size empty in the parameter list. All lesser sizes (say in 3D, 4D arrays) must be specified. This is because the compiler must be able to know how far in memory it is from the beginning of one row to the beginning of the next. It does not need to explicitly know how many rows there are. In this way, your 2D array handling function can be used with different arrays of any number of rows, as long as they have the same number of columns. You will generally pass the number of rows as an additional parameter to your function.

If your task is just to fill the array, then simple nested for loops is the best solution, both in terms of simplicity and performance.

Can you elaborate on the actual problem statement?

[ihatestarch]

I only WISH I could use nested for loops for this problem.

The actual problem? I need to write a recursive function that changes the contents of a 2D array. Main.cpp creates that array and fills it with 1's. I must add the first two numbers and place the answer in the matrix below the second number.

I hope I don't sound too confusing. My for loop does this problem fine:

for(int i=0; i<10; i++)
    {
        for(int j=0; j<10; j++)
        {
            array[i+1][j+1] = array[i][j] + array[i][j+1];
             cout << array[i][j] << "    ";
        }
        cout << endl;
    }

I want to figure out the code recursively, but I don't have a clue how to set up the function so that I can manipulate the rows and columns like I did in the for loop or what the process might appear like in main.

Thanks for the explanation of the 2D array bracket values btw.

[Sky Diploma]

I think you will basically need a square matrix, ie: no. of columns = no. of rows. then, You could do somthing like this

Well the recursive function might be applied on only the last row.

you could say somthing like

val(x,y)=val(x-1,y-1)+val(x-1,y);

This would be the function which should end return val = 1 if the position of x or y is out of bounds.....

Hope this is the solution you are looking for.

The Problem is that only half of the area will be filled(correctly) by this function if we execute it for the last element.

[ihatestarch]

Well the recursive function might be applied on only the last row.

you could say somthing like

val(x,y)=val(x-1,y-1)+val(x-1,y);

This would be the function which should end return val = 1 if the position of x or y is out of bounds.....

Hope this is the solution you are looking for.

The Problem is that only half of the area will be filled(correctly) by this function if we execute it for the last element.

I knew the formula would look like that, it's just like the loop almost. But I was a bit foggy on the base case. So, when I call a function in main, will the code display like this?

arrayfunction(array, row, col);
    
    for(int i=0; i<row; i++)
    {
        for(int j=0; j<col; j++)
        {
            cout << array[i][j] << "   ";
        }
        cout << endl;
    }

And would the function return an int or would it be void? I'm thinking I pass by reference by using void because I'd use it if I were using a for loop in my function. I'm new to recursion so I'm not sure.