C++ Exception Minimax algorithm for Tictactoe

Question

I'm trying to make a simple AI for playing tictactoe, but it is not working; I get an 'std::out_of_range' when the board fills up (brute forcing till the first final nodes of the first branch), and I quite didn't find a solution.

If I play X at 0,0 it crashes on the return of the best move return jogadas.at(melhorMov); // return best move after the 10th iteration.

(full code for Windows MingW here if you wish )

(the shown games above it's the bruteforcing steps, not the actual game)

AI algorithm:

Moving/launching AI

void IA::movimenta(){ //lauches the AI move action
    std::cout << "**Pensando**" << std::endl; //little message
    pensamentos = 0;                          //counter of iterations
    cmp = campo.getcampo();                   //gets the pointer** to the tictactoe field
    AiMove jogada = MelhorJogada(AIjogador);  //gets the best move for the AIplayer
    campo.joga(AIjogador,jogada.x,jogada.y);  //puts the best move on the field
}

Minimax Code

#include "ia.h"
#include <vector>
#include <iostream>

using namespace std;

IA::IA()
{

}


void IA::inicia(field &campo, field::jogador IAplayer){
    this->campo = campo;

    this->AIjogador = IAplayer;
    if(IAplayer == field::x){
        this->HUjogador = field::o;
    }else{
        this->HUjogador = field::x;
    }

}


void printacamp(field::campo **campo){
    cout << "  0 1 2" << endl;
    for (int var = 0; var < 3; ++var) {
        cout << var;
        cout << "|";
        for (int var2 = 0; var2 < 3; ++var2) {

            switch (campo[var][var2]) {
            case field::NADA:
                cout << " ";
                break;
            case field::x_c:
                cout << "X";
                break;
            case field::o_c:
                cout << "O";
                break;
            default:
                break;
            }

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

void IA::movimenta(){ //lauches the AI move action
    std::cout << "**Pensando**" << std::endl; //little message
    pensamentos = 0;                          //couter of iterations
    cmp = campo.getcampo();                   //gets the pointer** to the tictactoe field
    AiMove jogada = MelhorJogada(AIjogador);  //gets the best move for the AIplayer
    campo.joga(AIjogador,jogada.x,jogada.y);  //puts the best move on the field
}

AiMove IA::MelhorJogada(field::jogador jogador){ //bruteforce through the possible moves and searches for the best one
    field::jogador vic = campo.checaJ(); // checks if someone wins the game (final node)
    if(vic == AIjogador){                //if AIplayer wins
        return AiMove(15);             //add 15 points
    } else if(vic == jogador){           //if human wins
        return AiMove(-15);            //add -15 points
    } else if(vic == field::NINGJ){      //if its a tie (full board no winners)
        return AiMove(0);               //score 0
    }                                  //if none of those, the game is still in progress
    std::vector<AiMove> jogadas;        //vector for moves, something tells me that it should be static but it gives alot of bugs and nosense moves (or no moves at all)
    AiMove jogada;                      //move for this iteration
    pensamentos++;                      //add counter
    cout << pensamentos << endl;        //print counter
    for (int y = 0; y < 3; ++y) {       //for each of the board
        for (int x = 0; x < 3; ++x) {
            if(cmp[x][y] == field::NADA){  // if its an empty space
                jogada.x = x;              //gets the x,y of the empty space
                jogada.y = y;
                campo.jogaJ(jogador,jogada.x,jogada.y); //makes a move

                printacamp(cmp);           //prints it on screen

                if(jogador == AIjogador){  //if its max(AI) next is human
                    jogada.pontos = MelhorJogada(HUjogador).pontos;
                }else{                     //if its min(Human) next is AI
                    jogada.pontos = MelhorJogada(AIjogador).pontos;
                }
                jogadas.push_back(jogada); //store the score of the final node
                campo.jogaJ(field::NADAJ,jogada.x,jogada.y); // delete the move made for testings
            }
        }
    }
    int melhorMov = 0;                  // bestMove is 0
    if(jogador == AIjogador){           // if AIturn(max)
        int melhorPon = -1000000;       // best pontuation = -∞
        for (int var = 0; var < jogadas.size(); ++var) { //best move/points of the subbranches
            if(jogadas.at(var).pontos > melhorPon){
                melhorMov = var;
                melhorPon = jogadas.at(var).pontos;
            }
        }
    } else {                            //if human(min)
        int melhorPon = 1000000;        //best pontution = +∞
        for (int var = 0; var < jogadas.size(); ++var) { //best move/points of the subbranches
            if(jogadas.at(var).pontos < melhorPon){
                melhorMov = var;
                melhorPon = jogadas.at(var).pontos;
            }
        }
    }
    return jogadas.at(melhorMov); // return best move

}

AI.h

#pragma once
#ifndef IA_H
#define IA_H
#include "field.h"
#include <vector>
struct AiMove {
    AiMove() {};
    AiMove(int Pontos) : pontos(Pontos) {}
    int x;
    int y;
    int pontos;
};


class IA
{

public:
        IA();
        void inicia(field &camp, field::jogador IAplayer);
        void movimenta();
private:
        field campo;
        AiMove MelhorJogada(field::jogador HUjogador);
        field::campo **cmp;
        field::jogador HUjogador;
        field::jogador AIjogador;
        int pensamentos = 0;

};
#endif // IA_H

if you are suggesting, yes i did try debbuging the code, but i could not find a way to fix it, or find the bug in the logic — Ollegn, Dec 14 '15 at 03:48
Please clearly indicate the line of code where the exception is thrown. — Neil Kirk, Dec 14 '15 at 03:54
if i play X at 0,0 it crashes on the return of the best move `return jogadas.at(melhorMov); // return best move` — Ollegn, Dec 14 '15 at 04:00

score 1 · Accepted Answer · answered Dec 14 '15 at 04:43

1

Your vector is empty (as it should be, there are no remaining legal moves).

Calling at(0) on an empty vector throws an exception, because there is no element 0.

answered Dec 14 '15 at 04:43

Ben Voigt

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actually there is positions at 0 but you are right, i set the initial condition to -1 and made a verification on the return and other modifications and it worked, thanks for your help – Ollegn Dec 14 '15 at 16:21
@Ollegn: I'm not talking about position (0, 0) on the board, but index 0 in the vector. When the vector is empty, 0 is not a legal index. – Ben Voigt Dec 14 '15 at 16:58
Im talking about the vectors, in c++ vectors starts at 0 and goes forth `Notice that the first element has a position of 0 (not 1).` [Font](http://www.cplusplus.com/reference/vector/vector/at/) – Ollegn Dec 14 '15 at 18:54
1

@Ollegn: You missed my point. Valid indexes have `i < size()`. When `size() == 0`, then `0` is not a valid index. – Ben Voigt Dec 14 '15 at 19:19
oh, got it, it's true, the size counting starts at 1, if no data is stored in the vector the size is 0. – Ollegn Dec 14 '15 at 19:26
1

@Ollegn: Right. `0` isn't a problem because of being too low (you are correct that indexing starts at `0` not `1`). It's a problem because it is too high, when the vector is empty. – Ben Voigt Dec 14 '15 at 19:27

C++ Exception Minimax algorithm for Tictactoe

1 Answers1