Rat Maze

How do I change the position to a different character so the rat will
not visit the same place over and over again?

/*

 */
#include <fstream>
#include <iostream>
#include "Matrix.h"
using namespace std;

struct Location
{
    int r, c;
    Location()
    {
        r = c = 0;
    }
};
class Maze: public Matrix
{
    private:

        Location rat;

    public:

        Maze(int r = 10, int c = 10): Matrix(r, c){}
        void moveRat(int r, int c);
        ostream& draw(ostream&);
        void solve(int r, int c);

};
/////////////////////////////////////////////
int main()
{
    ifstream file;
    Maze *maze;
    int r, c;
    char data;
    file.open("maze.txt");
    file >> r >> c;
    maze = new Maze(r, c);
    file >> r >> c;
    maze->moveRat(r, c);

    for ( r = 0; r < maze->getRows(); r++)
    {
        for ( c = 0; c < maze->getColumns(); c++)
        {
            file >> data;
            (*maze)[r][c] = data-'0';
        }
    }

    maze->draw(cout);
    maze->solve(r, c);
    cout << '\n';
    cout << '\n';
    maze->draw(cout);

    return 0;
}
/////////////////////////////////////////////

void Maze :: moveRat(int r, int c)
{
    rat.r = r;
    rat.c = c;
}

ostream& Maze :: draw(ostream& out)
{

    for ( int r = 0; r < rows; r++)
    {
        for ( int c = 0; c < cols; c++)
        {
            if(r == rat.r && c == rat.c)
            {
                out << 'R';
            }
            else
            {
                out << element[r][c];
            }
        }
        out << endl;
    }
    //out << element[9][9];
    return out;
}

void Maze :: solve(int r, int c)
{
    //r = rat.r;
    //c = rat.c;
    if ( element[rat.r + 1][rat.c] == 0)
    {
        cout << "move up" << endl;
        moveRat(rat.r + 1, rat.c);
        //element[rat.r][rat.c] = 'V';
        solve(rat.r + 1, rat.c);
    }

    if ( element[rat.r][rat.c + 1] == 0)
    {
        cout << "move right" << endl;
        moveRat(rat.r, rat.c + 1);
        //element[rat.r][rat.c] = 'V';
        solve(rat.r, rat.c + 1);
    }

    if ( element[rat.r - 1][rat.c] == 0)
    {
        cout << "move down" << endl;
        moveRat(rat.r - 1, rat.c);
        //element[rat.r][rat.c] = 'V';
        solve(rat.r -1, rat.c);
    }

    if ( element[rat.r][rat.c - 1] == 0)
    {
        cout << "move left" << endl;
        moveRat(rat.r, rat.c - 1);
        //element[rat.r][rat.c] = 'V';
        solve(rat.r, rat.c - 1);
    }

    else
    {
        cout << "You have nowhere to go rat!" << endl;
    }
}