Program should run... fatal error LNK1120 and error LNK2019 - c++

Question

We were given a header and cpp file for our next project from which we need to derive a class. These two files should work properly "out of the box" but for some reason I'm getting these errors and clicking on the errors doesn't take me anywhere. I'm guessing it's a version problem since most of the books programs are of extension .cxx and we're working with .cpp, but I'm pretty new to programming so I don't know for sure. Also, most of the books other programs worked just fine in VS 2012. I'm using Visual Studio 2012 on Windows 7 64bit if that helps.
Errors:
1>MSVCRTD.lib(crtexe.obj) : error LNK2019: unresolved external symbol _main referenced in function ___tmainCRTStartup
1>Projects\Project 5\Debug\Project 5.exe : fatal error LNK1120: 1 unresolved externals
Here is the code for the header and cpp of our base class and thanks for the help guys:
Header:
#ifndef MAIN_SAVITCH_GAME
#define MAIN_SAVITCH_GAME
#include <queue> // Provides queue<string>
#include <string> // Provides string
namespace main_savitch_14
{
class game
{
public:
// ENUM TYPE
enum who { HUMAN, NEUTRAL, COMPUTER }; // Possible game outcomes
// CONSTRUCTOR and DESTRUCTOR
game( ) { move_number = 0; }
virtual ~game( ) { }
// PUBLIC MEMBER FUNCTIONS
// The play function should not be overridden. It plays one game,
// with the human player moving first and the computer second.
// The computer uses an alpha-beta look ahead algorithm to select its
// moves. The return value is the winner of the game (or NEUTRAL for
// a tie).
who play( );
protected:
// *******************************************************************
// OPTIONAL VIRTUAL FUNCTIONS (overriding these is optional)
// *******************************************************************
virtual void display_message(const std::string& message) const;
virtual std::string get_user_move( ) const;
virtual who last_mover( ) const
{ return (move_number % 2 == 1 ? HUMAN : COMPUTER); }
virtual int moves_completed( ) const { return move_number; }
virtual who next_mover( ) const
{ return (move_number % 2 == 0 ? HUMAN : COMPUTER); }
virtual who opposite(who player) const
{ return (player == HUMAN) ? COMPUTER : HUMAN; }
virtual who winning( ) const;
// *******************************************************************
// VIRTUAL FUNCTIONS THAT MUST BE OVERRIDDEND:
// The overriding function should call the original when it finishes.
// *******************************************************************
// Have the next player make a specified move:
virtual void make_move(const std::string& move) { ++move_number; }
// Restart the game from the beginning:
virtual void restart( ) { move_number = 0; }
// *******************************************************************
// PURE VIRTUAL FUNCTIONS
// *******************************************************************
// (these must be provided for each derived class)
// Return a pointer to a copy of myself:
virtual game* clone( ) const = 0;
// Compute all the moves that the next player can make:
virtual void compute_moves(std::queue<std::string>& moves) const = 0;
// Display the status of the current game:
virtual void display_status( ) const = 0;
// Evaluate a board position:
// NOTE: positive values are good for the computer.
virtual int evaluate( ) const = 0;
// Return true if the current game is finished:
virtual bool is_game_over( ) const = 0;
// Return true if the given move is legal for the next player:
virtual bool is_legal(const std::string& move) const = 0;
private:
// MEMBER VARIABLES
int move_number; // Number of moves made so far
// STATIC MEMBER CONSTANT
static const int SEARCH_LEVELS = 4; // Levels for look-ahead evaluation
// PRIVATE FUNCTIONS (these are the same for every game)
int eval_with_lookahead(int look_ahead, int beat_this);
void make_computer_move( );
void make_human_move( );
};
}
#endif
CPP:
#include <cassert> // Provides assert
#include <climits> // Provides INT_MAX and INT_MIN
#include <iostream> // Provides cin, cout
#include <queue> // Provides queue<string>
#include <string> // Provides string
#include "game.h" // Provides definition of game class
using namespace std;
namespace main_savitch_14
{
//*************************************************************************
// STATIC MEMBER CONSTANTS
const int game::SEARCH_LEVELS;
//*************************************************************************
// PUBLIC MEMBER FUNCTIONS
game::who game::play( )
// The play function should not be overridden. It plays one round of the
// game, with the human player moving first and the computer second.
// The return value is the winner of the game (or NEUTRAL for a tie).
{
restart( );
while (!is_game_over( ))
{
display_status( );
if (last_mover( ) == COMPUTER)
make_human_move( );
else
make_computer_move( );
}
display_status( );
return winning( );
}
//*************************************************************************
// OPTIONAL VIRTUAL FUNCTIONS (overriding these functions is optional)
void game::display_message(const string& message) const
{
cout << message;
}
string game::get_user_move( ) const
{
string answer;
display_message("Your move, please: ");
getline(cin, answer);
return answer;
}
game::who game::winning( ) const
{
int value = evaluate( ); // Evaluate based on move that was just made.
if (value > 0)
return COMPUTER;
else if (value < 0)
return HUMAN;
else
return NEUTRAL;
}
//*************************************************************************
// PRIVATE FUNCTIONS (these are the same for every game)
int game::eval_with_lookahead(int look_ahead, int beat_this)
// Evaluate a board position with lookahead.
// --int look_aheads: How deep the lookahead should go to evaluate the move.
// --int beat_this: Value of another move that we’re considering. If the
// current board position can't beat this, then cut it short.
// The return value is large if the position is good for the player who just
// moved.
{
queue<string> moves; // All possible opponent moves
int value; // Value of a board position after opponent moves
int best_value; // Evaluation of best opponent move
game* future; // Pointer to a future version of this game
// Base case:
if (look_ahead == 0 || is_game_over( ))
{
if (last_mover( ) == COMPUTER)
return evaluate( );
else
return -evaluate( );
}
// Recursive case:
// The level is above 0, so try all possible opponent moves. Keep the
// value of the best of these moves from the opponent's perspective.
compute_moves(moves);
assert(!moves.empty( ));
best_value = INT_MIN;
while (!moves.empty( ))
{
future = clone( );
future->make_move(moves.front( ));
value = future->eval_with_lookahead(look_ahead-1, best_value);
delete future;
if (value > best_value)
{
if (-value <= beat_this)
return INT_MIN + 1; // Alpha-beta pruning
best_value = value;
}
moves.pop( );
}
// The value was calculated from the opponent's perspective.
// The answer we return should be from player's perspective, so multiply times -1:
return -best_value;
}
void game::make_computer_move( )
{
queue<string> moves;
int value;
int best_value;
string best_move;
game* future;
// Compute all legal moves that the computer could make.
compute_moves(moves);
assert(!moves.empty( ));
// Evaluate each possible legal move, saving the index of the best
// in best_index and saving its value in best_value.
best_value = INT_MIN;
while (!moves.empty( ))
{
future = clone( );
future->make_move(moves.front( ));
value = future->eval_with_lookahead(SEARCH_LEVELS, best_value);
delete future;
if (value >= best_value)
{
best_value = value;
best_move = moves.front( );
}
moves.pop( );
}
// Make the best move.
make_move(best_move);
}
void game::make_human_move( )
{
string move;
move = get_user_move( );
while (!is_legal(move))
{
display_message("Illegal move.\n");
move = get_user_move( );
}
make_move(move);
}
}

Answer 1

You don't have int main() function. Every program must have this.
http://en.wikipedia.org/wiki/Main_function

Answer 2

They may compile properly out of the box but, without a main function, they won't link or run.
You need to combine them with your own source code, which I would expect to contain at least a main function which used those classes somehow. As a first step, start with:
int main(void) {
return 0;
}
That won't do anything useful but it should get you over the immediate link errors.