How do I pass an array to a constructor?

In this case it might be best to use a reference to the array:

class board{    int (&state)[64];public:    board(int (&arr)[64])         : state(arr)    {}    // initialize use a pointer to an array    board(int (*p)[64])         : state(*p)    {}    void print();};

A couple of advantages - no copying of the array, and the compiler will enforce that the correct size array is passed in.

The drawbacks are that the array you initialize the board object with needs to live at least as long as the object and any changes made to the array outside of the object are 'reflected' into the object's state. but those drawbacks occur if you use a pointer to the original array as well (basically, only copying the array will eliminate those drawbacks).

One additional drawback is that you can't create the object using a pointer to an array element (which is what array function parameters 'decay' to if the array size isn't provided in the parameter's declaration). For example, if the array is passed through a function parameter that's really a pointer, and you want that function to be able to create a board object referring to that array.

Attempting to pass an array to a function results in passing a pointer to the first element of the array.

You can't assign arrays, and taking a parameter like T[] is the same as T*. So

*state = *arr;

Is dereferencing the pointers to state and arr and assigning the first element of arr to the first element of state.

If what you want to do is copy the values from one array to another, you can use std::copy:

std::copy(arr, arr + 64, state); // this assumes that the array size will                                 // ALWAYS be 64

Alternatively, you should look at std::array<int>, which behaves exactly like you were assuming arrays behave:

#include <array>#include <algorithm>#include <iostream> class board{    public:        std::array<int, 64> state;        board(const std::array<int, 64> arr) // or initialiser list : state(arr)        {            state = arr; // we can assign std::arrays        }        void print();};void board::print(){    for (int y=0; y<8; y++)    {        for (int x=0; x<8; x++)            std::cout << state[x + y*8] << " ";        std::cout << "\n";    }}int main(){    // using this array to initialise the std::array 'test' below    int arr[] = {        0, 1, 2, 3, 4, 5, 6, 7,        1, 2, 3, 4, 5, 6, 7, 8,        2, 3, 4, 5, 6, 7, 8, 9,        3, 4, 5, 6, 7, 8, 9,10,        4, 5, 6, 7, 8, 9,10,11,        5, 6, 7, 8, 9,10,11,12,        6, 7, 8, 9,10,11,12,13,        7, 8, 9,10,11,12,13,14 };    std::array<int, 64> test(std::begin(arr), std::end(arr));    board b(test);    b.print();    std::cin.get();    return 0;}

#include <iostream>class board{    public:        int * state;    //changed here, you can also use **state        board(int *arr)               //changed here        {          state = arr;        }        void print();};void board::print(){    for (int y=0; y<8; y++)    {        for (int x=0; x<8; x++)            std::cout << *(state + x + y*8) << " ";   //changed here        std::cout << "\n";    }}int main(){    int test[64] = {        0, 1, 2, 3, 4, 5, 6, 7,        1, 2, 3, 4, 5, 6, 7, 8,        2, 3, 4, 5, 6, 7, 8, 9,        3, 4, 5, 6, 7, 8, 9,10,        4, 5, 6, 7, 8, 9,10,11,        5, 6, 7, 8, 9,10,11,12,        6, 7, 8, 9,10,11,12,13,        7, 8, 9,10,11,12,13,14 };    board b(test);    b.print();    std::cin.get();    return 0;}

or you can use it as:

class board{    public:        int state[64];        board(int arr[])        {            for(int i=0;i<64;++i)               state[i] = arr[i];        }        void print();};

EDIT 1:stable solution

class board    {        public:            int * state;    //changed here, you can also use **state            board(int *arr)               //changed here            {              state = new int[64];              for(int i=0;i<64;++i)                   state[i] = arr[i];            }            void print();    };