Unable to generate random numbers when passed into a function in C++

I'm still a beginner trying to learn some C++.

I'm trying to pass in a random number to a function to generate a random 2D array for a small game. Unfortunately, it always prints out the same option instead of generating a random one each time.

Could you please help? I'd appreciate it.

Could you please advise me also if there is a better way to randomize 'X' and 'O' within a 2D array than simply hard-coding it as I have tried?

Thank you very much.

#include <iostream>
#include <cstdlib>

using namespace std;

void generateBlock(int n)
{
    switch (n)
    {
    case 0:
    {
        char blocks1[4][4] = { 'X', 'X', 'O', 'O',
            'X', 'X', 'O', 'O',
            'O', 'O', 'O', 'O',
            'O', 'O', 'O', 'O' };

        for (int i = 0; i < 4; i++)
        {
            for (int j = 0; j < 4; j++)
            {
                cout << blocks1[i][j];
            }
            cout << endl;
        }
        return;
    }

    case 1:
    {
        char blocks2[4][4] = { 'X', 'X', 'O', 'O',
            'O', 'O', 'X', 'X',
            'O', 'O', 'O', 'O',
            'O', 'O', 'O', 'O' };

        for (int i = 0; i < 4; i++)
        {
            for (int j = 0; j < 4; j++)
            {
                cout << blocks2[i][j];
            }
            cout << endl;
        }
        return;
    }

    case 2:
    {
        char blocks3[4][4] = { 'X', 'X', 'O', 'O',
            'X', 'O', 'O', 'O',
            'X', 'O', 'O', 'O',
            'O', 'O', 'O', 'O' };

        for (int i = 0; i < 4; i++)
        {
            for (int j = 0; j < 4; j++)
            {
                cout << blocks3[i][j];
            }
            cout << endl;
        }
        return;
    }
    }
}

int main()
{
    int n = rand() % 3;
    generateBlock(n);
}