Passing Dynamic Two Dimensional Array as argument to a functoin in c++

Question

Hy guys, I actually Trying to create a 2D Array in c++ but not able to create that, When I execute the following statement

int arr=new int[10][10]

It gives me error and when I search on google it shows me 2D array in c++ is array of pointers which is declare like the below statements

int** a = new int*[rowCount];
for(int i = 0; i < rowCount; ++i)
    a[i] = new int[colCount];

I got the logic which is a is a pointer to pointer to the matrix but now I am not able understand the logic like how can i point to the data on this matrix, Suppose to see the number store in index a[0][0] should i write

cout<<a[0][0]

or not, I am not able to get the logic how this pointer to pointer will work when with the pointers pointing to the matrix, and one more thing is that I am not able to pass it as an argument to a function. The code for passing it as a parameter is given below

void displayArray(int a[10][10])
{
        for (int i=0; i<10; i++)
    {
        for(int j=0; j<10; j++)
        {
            cout<<*a[i][j]<<"\t";
        }
        cout<<endl;
    }
}

int main()
{
    int** a = new int*[10];
    for(int i = 0; i < 10; ++i)
        a[i] = new int[10];

    displayArray(**a);
}

It giving me the following error

error: invalid conversion from ‘int’ to ‘int (*)[10]’ [-fpermissive]

Actually I am not able to get any sense of how to use the pointer to pointer in a matrix, it's too complex compared to other languages where we just need to use new operator and can access them with their dimensions, No need of this pointer to pointer concept. Please help me understanding the whole logic of this 2d dynamic array of c++.

Pop quiz: what is the type of `a`? That's the same type that the parameter to your `displayArray` must be. — Sam Varshavchik, Oct 18 '20 at 03:32
Question and answers would have more clarity if the sizes where different like `int[10][20]`. Unfortunate they are the same. — chux - Reinstate Monica, Oct 18 '20 at 03:48
*I actually Trying to create a 2D Array in c++ but not able to create that* -- [A much better way to do what you are asking](https://stackoverflow.com/questions/21943621/how-to-create-a-contiguous-2d-array-in-c/21944048#21944048) — PaulMcKenzie, Oct 18 '20 at 04:21
***"it's too complex compared to other languages"*** - This is not a necessarily a completely fair comparison. Most other languages simply can not so this. It is out of their scope. These are very low level array constructs that even most `C++` programmers never need to use. For something more equivalent to a dynamic array in another language you should look at `std::vector` for an array and `std::vector>` for a 2D array of arrays. — Galik, Oct 18 '20 at 04:32

Juned Khan · Accepted Answer · 2020-10-18T03:43:50.270

you need to get the parameter in your function as pointer

void displayArray(int **a)
{
        for (int i=0; i<10; i++)
    {
        for(int j=0; j<10; j++)
        {
            cout<< a[i][j] <<"\t";
        }
        cout<<endl;
    }
}

int main()
{
    int** a = new int*[10];
    for(int i = 0; i < 10; ++i)
        a[i] = new int[10];

    displayArray(a);
}

it prints 10 rows and columns of value 0 because the 2D array is uninitialized

Passing Dynamic Two Dimensional Array as argument to a functoin in c++

1 Answers1