How can i have player two choose a random slot in tic tac toe

[dream1123]

#include "pch.h"
#include <iostream>
#include <string>
#include <ctime>
using namespace std;

//Array used to store data on the board
char square[10] = { 'o','1','2','3','4','5','6','7','8','9' };

int systemcheck();
void board();

int main()
{
//Defining variables
int player = 1, i, choice;
//playermark is used for switching the slot number with an X or O
char playermark;
do
{
board();
player = (player % 2) ? 1 : 2;

cout << "Player " << player << ", enter a number: ";
cin >> choice;

playermark = (player == 1) ? 'X' : 'O';

if (choice == 1 && square[1] == '1')

square[1] = playermark;
else if (choice == 2 && square[2] == '2')

square[2] = playermark;
else if (choice == 3 && square[3] == '3')

square[3] = playermark;
else if (choice == 4 && square[4] == '4')

square[4] = playermark;
else if (choice == 5 && square[5] == '5')

square[5] = playermark;
else if (choice == 6 && square[6] == '6')

square[6] = playermark;
else if (choice == 7 && square[7] == '7')

square[7] = playermark;
else if (choice == 8 && square[8] == '8')

square[8] = playermark;
else if (choice == 9 && square[9] == '9')

square[9] = playermark;
else
{
//if the input does not equal any integer listed in the strings, the if statement will register the character as invalid
cout << "Invalid character || somebody has already played that slot!";

player--;
cin.ignore();
cin.get();
//after move is performed
}
i = systemcheck();
//After move system is checking for a win
player++;
//Game win/tie loop
} while (i == -1);
board();
if (i == 1)

cout << "==>\aPlayer " << --player << " win ";
else
cout << "==>\aPlayer 1 & Player 2 has tied";

cin.ignore();
cin.get();
return 0;
}

//Board drawn with console outputs, will return no value
void board()
{
cout << "\n\n\tTICTACTOE\n\n";

cout << "Player 1 - X - Player 2 - O -" << endl << endl;
cout << endl;
//Defines where a specific slot is placed increasing in a row
cout << " | | " << endl;
cout << " " << square[1] << " | " << square[2] << " | " << square[3] << endl;

cout << "_____|_____|_____" << endl;
cout << " | | " << endl;

cout << " " << square[4] << " | " << square[5] << " | " << square[6] << endl;

cout << "_____|_____|_____" << endl;
cout << " | | " << endl;

cout << " " << square[7] << " | " << square[8] << " | " << square[9] << endl;

cout << " | | " << endl << endl;
}



//Will check if a given player has a winning board
int systemcheck()
{
if (square[1] == square[2] && square[2] == square[3])
//Check win verifying if any given slot has a matching slot, otherwise performing three slots in a row or column
return 1;
else if (square[4] == square[5] && square[5] == square[6])

return 1;
else if (square[7] == square[8] && square[8] == square[9])

return 1;
else if (square[1] == square[4] && square[4] == square[7])

return 1;
else if (square[2] == square[5] && square[5] == square[8])

return 1;
else if (square[3] == square[6] && square[6] == square[9])

return 1;
else if (square[1] == square[5] && square[5] == square[9])

return 1;
else if (square[3] == square[5] && square[5] == square[7])

return 1;
else if (square[1] != '1' && square[2] != '2' && square[3] != '3'
&& square[4] != '4' && square[5] != '5' && square[6] != '6'
&& square[7] != '7' && square[8] != '8' && square[9] != '9')

return 0;
else
return -1;
}

[jonnin]

set up a table of the locations and when either side uses a location, mark it used.
eg
bool table[9] = {false};
then you can use <random> to get a value from 0-8 in a loop until you get an empty location. This is woefully inefficient when there is only 1 slot left, but computers are fast enough that it still only takes a few ms to do it this way. Its slightly harder to do it without the brute force; you can generate a unique random list (permutation really) of the values 0-8 and just iterate that, if a location is used, go to next one.

[nuderobmonkey]

Another way is, determining how many fields are empty and randomizing over that number. Lets' assume the random number is named 'r', then you could use the 'r'-th free field.