C++ Tic Tac Toe AI Help!?

[NRoth]

I am in a C++ programming class right now, and I'm stuck. I made a Tic Tac Toe game (as shown below) that needs two players..I would like to change this program, so that Instead of player 2 getting a chance to enter a move, the computer will mark an 'o' and act as player 2. I really need some help guys! any input would be much appreciated.

// Include the libraries
#include <iostream>
#include <string>
 
//Use the standard namespace
using namespace std;
 
// Declare global variables
char Board[9];
 
// Declare functions
void showBoard ( );
bool moveIsValid (int m);
int whoWon ( ); //Returns 0 if no one has won, 1 if player 1 has won, and 2 if player 2 has won
 
void main ( )
{
   // Declare local variables
   string Player_1_Name;
   string Player_2_Name;
   int Whose_Turn = 1; // 1 means it's player 1's turn, 2 means it's player 2's turn
   int Move; // Stores where the player wants to move
   int Total_Moves = 0;
 
   //Assign values to the playing board
   Board[0] = '0';
   Board[1] = '1';
   Board[2] = '2';
   Board[3] = '3';
   Board[4] = '4';
   Board[5] = '5';
   Board[6] = '6';
   Board[7] = '7';
   Board[8] = '8';
 
   // Get player names
   cout << "Player 1: Please enter your name." << endl;
   cin >> Player_1_Name;
   cout << "Player 2: Please enter your name." << endl;
   cin >> Player_2_Name;
 
   while (whoWon ( ) == 0 && Total_Moves < 9)
   {
      // Do this until the player chooses a valid move
      do
      {
         // Show the board
         showBoard ( );
 
         // Tell which player to move
         if (Whose_Turn == 1)
         {
            cout << Player_1_Name << ": It's your turn." << endl;
         }
         else
         {
            cout << Player_2_Name << ": It's your turn." << endl;
         }
         // Get the move
         cout << "Enter the number of the spot where you'd like to move." << endl;
         cin >> Move;
      } while (moveIsValid (Move) != true);
 
      // Add 1 to Total_Moves
      Total_Moves++;
 
      // Change whose turn it is
      switch (Whose_Turn)
      {
      case (1):
         {
            Board[Move] = 'x';
            Whose_Turn = 2;
            break;
         }
      case (2):
         {
            Board[Move] = 'o';
            Whose_Turn = 1;
         }
      }
   }
   // Show the board
   showBoard ( );
 
   if (whoWon ( ) == 1)
   {
      cout << Player_1_Name << " has won the game!" << endl;
   }
   else if (whoWon ( ) == 2)
   {
      cout << Player_2_Name << " has won the game!" << endl;
   }
   else
   {
      cout << "It's a tie game!" << endl;
   }
 
   system ("PAUSE");
}
 
void showBoard ( )
{
   cout << endl;
   cout << Board[0] << " | " << Board[1] << " | " << Board[2] << endl;
   cout << "--+---+--" << endl;
   cout << Board[3] << " | " << Board[4] << " | " << Board[5] << endl;
   cout << "--+---+--" << endl;
   cout << Board[6] << " | " << Board[7] << " | " << Board[8] << endl;
   cout << endl;
}
 
bool moveIsValid (int m)
{
   if (Board[m] != 'x' && Board[m] != 'o')
   {
      return true;
   }
   else
   {
      return false;
   }
}
 
int whoWon ( )
{
   if (Board[0] == Board[1] && Board[1] == Board[2])
   {
      if (Board[0] == 'x')
      {
         return 1;
      }
      else
      {
         return 2;
      }
   }
   if (Board[3] == Board[4] && Board[4] == Board[5])
   {
      if (Board[3] == 'x')
      {
         return 1;
      }
      else
      {
         return 2;
      }
   }
   if (Board[6] == Board[7] && Board[7] == Board[8])
   {
      if (Board[6] == 'x')
      {
         return 1;
      }
      else
      {
         return 2;
      }
   }
   if (Board[0] == Board[3] && Board[3] == Board[6])
   {
      if (Board[0] == 'x')
      {
         return 1;
      }
      else
      {
         return 2;
      }
   }
   if (Board[1] == Board[4] && Board[4] == Board[7])
   {
      if (Board[1] == 'x')
      {
         return 1;
      }
      else
      {
         return 2;
      }
   }
   if (Board[2] == Board[5] && Board[5] == Board[8])
   {
      if (Board[2] == 'x')
      {
         return 1;
      }
      else
      {
         return 2;
      }
   }
   if (Board[0] == Board[4] && Board[4] == Board[8])
   {
      if (Board[0] == 'x')
      {
         return 1;
      }
      else
      {
         return 2;
      }
   }
   if (Board[2] == Board[4] && Board[4] == Board[6])
   {
      if (Board[2] == 'x')
      {
         return 1;
      }
      else
      {
         return 2;
      }
   }
   return 0;
}

[MiiNiPaa]

Make an array of all possible moves and make computer choose randomly one.

[writetonsharma]

work on the game tree... for tic tac toe a game tree would be very small...
a game tree makes all the possible moves and then on that move what all moves the opponent can play.. and then choose the best out of these.

the steps can go till multiple levels deep on the basis of time available to play the move... But for beginning, one level deep would give good results.. multiple levels are necessary for chess..