more tic tac toe

I don't understand the description in English of what you are trying to do. Perhaps you can try to explain it with an example?

ok I am trying to check for a empty spot on a tic tac toe board and then put an X or O in that spot.I dont want the computer to put a O in an already occupied spot.

One reasonable method consist of making a list of the empty spaces, then pick a random one from those.

Do you need to see code for that?

cool yes a little bit of code would help.

There you go:
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <vector>

enum Piece {Empty, Cross, Nought};

class Board {
Piece array[9];

public:
Board() {
for (int i=0; i<9; ++i)
array = Empty;
}

void make_move(int square, Piece piece) {
array[square] = piece;
}

int pick_random_empty_square() {
std::vector<int> empties;
empties.reserve(9);
for (int i=0; i<9; ++i) {
if (array == Empty)
empties.push_back(i);
}

int random_index = std::rand() % empties.size();

return empties[random_index];
}

friend std::ostream &operator<<(std::ostream &os, Board const &board);
};

std::ostream &operator<<(std::ostream &os, Board const &board) {
for (int row=0; row<3; ++row) {
for (int col=0; col<3; ++col)
os << "_XO"[board.array[3*row+col]] << ' ';
os << '\n';
}
return os;
}

int main() {
std::srand(std::time(0));

Board board;

for (int i=0; i<9; ++i) {
board.make_move(board.pick_random_empty_square(), i%2==0 ? Cross : Nought);
std::cout << board << '\n';
}
}


If all you're actually trying to do is find the first empty space and replace it with an O then this would do it:



//Set all spaces to ' ' when you initialize the board
for (int i = 0; i < 8; ++i) //Where 8 is the size of the board
{
board = ' ';
}

//Then when you're wanting to replace the first empty space wth 'O'
for (int i = 0; i < 8; ++i)
{
if (board == ' ')
board = 'O';
}


If all you're actually trying to do is find the first empty space and replace it with an O then this would do it:

//Set all spaces to ' ' when you initialize the board
for (int i = 0; i < 8; ++i) //Where 8 is the size of the board
{
board = ' ';
}
//Then when you're wanting to replace the first empty space wth 'O'
for (int i = 0; i < 8; ++i)
{
if (board == ' ')
board = 'O';
}


if you do not put a break in that if statement, it will change ALL empty spaces into O's, rather than the first one you find

If (board =='')
{
board = 'O';
break;
}

that way only one empty is changed

also i think you may want 9 instead of 8; arent there 9 tiles in TTT?

[quote name='littletray26' timestamp='1350595688' post='4991555']
If all you're actually trying to do is find the first empty space and replace it with an O then this would do it:

//Set all spaces to ' ' when you initialize the board
for (int i = 0; i < 8; ++i) //Where 8 is the size of the board
{
board = ' ';
}
//Then when you're wanting to replace the first empty space wth 'O'
for (int i = 0; i < 8; ++i)
{
if (board == ' ')
board = 'O';
}


if you do not put a break in that if statement, it will change ALL empty spaces into O's, rather than the first one you find

If (board =='')
{
board = 'O';
break;
}

that way only one empty is changed

also i think you may want 9 instead of 8; arent there 9 tiles in TTT?
[/quote]

You're right, I forgot to put that break in there. Thank you for correcting that

Also, 0 is counted as a space so in an 8 space array there is in fact 9 spaces.

[quote name='littletray26' timestamp='1350595688' post='4991555']
If all you're actually trying to do is find the first empty space and replace it with an O then this would do it:

//Set all spaces to ' ' when you initialize the board
for (int i = 0; i < 8; ++i) //Where 8 is the size of the board
{
board = ' ';
}
//Then when you're wanting to replace the first empty space wth 'O'
for (int i = 0; i < 8; ++i)
{
if (board == ' ')
board = 'O';
}


if you do not put a break in that if statement, it will change ALL empty spaces into O's, rather than the first one you find

If (board =='')
{
board = 'O';
break;
}

that way only one empty is changed

also i think you may want 9 instead of 8; arent there 9 tiles in TTT?
[/quote]

is there anyway I can generate a random number only once and do not have it repeat.

is there anyway I can generate a random number only once and do not have it repeat.

If you mean produce a sequence of numbers where no number is repeated, like 3, 1, 9, 5, 2, 4, ... then sure, it's very easy:

1. generate an array [0, 1, 2, 3, 4, ... as much as you need, pretty much put the numbers you want in there]
2. for each element A in the array...
----> select a random element B in the array
----> swap elements A and B
3. iterate through the modified array to get your repeat-free random numbers

See Fisher-Yates shuffle. Is this what you meant?

yes thanks

Note the algorithm I posted is the naive, inefficient one. The correct one is given on Wikipedia and is much faster:

[source lang="plain"]To shuffle an array a of n elements (indices 0..n-1):
for i from n ? 1 downto 1 do
j ? random integer with 0 ? j ? i
exchange a[j] and a[/source]

Also, 0 is counted as a space so in an 8 space array there is in fact 9 spaces.

How can there be 9 spaces in an array of size 8? That makes no sense.

Arkane7 was correct. You will need to change that 8 to a 9. Otherwise, you can change the < sign to <= .

well i have found an algorithm that might work

#include <iostream>
#include <ctime>
using namespace std;
bool isContained(int arr[],int n,int x)
{
for(int i=0;i<n;i++)
{
if(arr==x)
return true;
}
return false;
}
int main()
{
srand(time(0));
const int x = 100;
int r[x];
for(int i=0;i<x;i++)
{
r=1+rand()%x;
while(isContained(r,i,r))
{
r=1+rand()%x;
}
}
for(int i=0;i<x;i++)
cout<<r<<"\n";
cout<<"\n\n";
return 0;
}


That is slow. I gave a link to the proper algorithm in my last post - why not use it? Since you want code:

[source lang="cpp"]#include < iostream>
#include < cstdlib>
#include < ctime>

using namespace std;

void fisherYates(int array[], int length)
{
/* Go over each element backwards. */
for (int t = length - 1; t != 0; t--)
{
/* Select random element in [0..t] */
int r = rand() % (t + 1);

/* Swap them. */
int tmp = array[t];
array[t] = array[r];
array[r] = tmp;
}
}

int main()
{
/* Randomize. */
srand(time(0));

/* Prepare array of N elements. */
const int length = 20;
int array[length];

/* Initialize it. */
for (int t = 0; t < length; ++t) array[t] = t;

/* Shuffle. */
fisherYates(array, length);

/* Print out array. */
for (int t = 0; t < length; ++t) cout < < array[t] < < " ";
cout < < endl;
}[/source]

(remove spaces between << as the source tags munch'em apparently)

cool thanks

[sub]

I have tried fisherYates shuffle but it still does not work.here is my code[/sub]

[sub]

void Computer::move_player_O()
{
srand(time(NULL)); [/sub]
[sub]

const int length=10;
int array[length];
for(int t=1;t<=9;t++)
array[t]=t;
fisherYates(array,length);
player_O=array[t];
t++;
}[/sub]
[sub]

[/sub]
[sub]

void Computer::check_player_O()
{
board[player_O]='O';
}[/sub]

Why are you incrementing t again inside the loop... the t++ inside the for construct already takes care of that

ok i took the t++ out but it still does not work,I am so close to fihishing,any more help would be great.