A matrix is simply data stored within a grid. It can be thought of as a multi-dimensional array, or “an array of arrays”. For example, a 2D array may also be referred to as a matrix (a table of rows and columns). And the initialization would look something like this

int matrix[2][3] = { { 1, 7 }, { 2, 9, 6 } };

When accessing data within a matrix imagine the matrix as a coordinate grid, and the numbers you give the matrix is the coordinate point of that data within the matrix.

Like arrays, Matrices are fixed in size. You allocate the memory for it when created and it cannot be changed.

The concept of recursion is actually simple but implementing it is more challenging than you might think. Recursion works by creating a function that calls itself until it hits a base case to end/breakout of the recursion function. Along with the base case, it has another case that slowly leads to the base case.

A simple implementation of this can be seen with a function that gets the factorial value given a certain number.

Here is what that function looks like:

// Factorial function using recursion
int factorial(int n)
{
    // Base case for when the number given is 0
    if (n == 0)
    {
        return 1;
    }
 
    // Takes the given value and multiplies it by the previous factorial value
    else
    {
        // Function calls itself (calls n-1) until it reaches the base case (0)
        return n * factorial(n - 1);
    }
}

As you can see the function starts with the base case and then actually implements the logic for the function. Let's give n a value of 3. First, we are going to check if n is 0 and when it fails that check it will return 3*factorial(2), and then it will evaluate when n is 2. This pattern will continue until it evaluates n being 0. Now that the function has not been called again it returns 1 because n is 0. Now factorial(1) can complete its return, then factorial(2), and finally factorial(3). The result of factorial(3) is 6.