I recently dug up an old C++ game I was making, and decided to continue development. I implemented an AI, intended on moving the NPCs towards the player, provided they are within a 20 square radius (it is a roguelike). However, instead of doing that, some NPCs disappear, while others will just freeze. What have I done wrong?

SeedRand();
                short NewX, NewY;
                if (player.getx()-this->Loc.X <= 20 && player.gety()-this->Loc.Y <= 20 && player.getx()-this->Loc.X >= -20 && player.gety()-this->Loc.Y >= -20)
                {
                        short Num = GetRandomNumber(0, 100);
                        if (player.getx()-this->Loc.X >= player.gety()-this->Loc.Y)
                        {
                                if (Num < 80)
                                {
                                        if (Num > 75)
                                        {
                                                if (player.getx()-this->Loc.X <= 0)
                                                {
                                                       NewX = 1;
                                                } else {
                                                       NewX = -1;
                                                }
                                        } else {
                                                if (player.getx()-this->Loc.X <= 0)
                                                {
                                                       NewX = -1;
                                                } else {
                                                       NewX = 1;
                                                }
                                        }
                                } else {
                                        if (Num > 95)
                                        {
                                                if (player.gety()-this->Loc.Y <= 0)
                                                {
                                                       NewY = 1;
                                                } else {
                                                       NewY = -1;
                                                }
                                        } else {
                                                if (player.gety()-this->Loc.Y <= 0)
                                                {
                                                       NewY = -1;
                                                } else {
                                                       NewY = 1;
                                                }
                                        }
                                }
                        } else {
                                if (Num < 80)
                                {
                                        if (Num > 75)
                                        {
                                                if (player.gety()-this->Loc.Y <= 0)
                                                {
                                                       NewY = 1;
                                                } else {
                                                       NewY = -1;
                                                }
                                        } else {
                                                if (player.gety()-this->Loc.Y <= 0)
                                                {
                                                       NewY = -1;
                                                } else {
                                                       NewY = 1;
                                                }
                                        }
                                } else {
                                        if (Num > 95)
                                        {
                                                if (player.getx()-this->Loc.X <= 0)
                                                {
                                                       NewX = 1;
                                                } else {
                                                       NewX = -1;
                                                }
                                        } else {
                                                if (player.getx()-this->Loc.X <= 0)
                                                {
                                                       NewX = -1;
                                                } else {
                                                       NewX = 1;
                                                }
                                        }
                                }
                        }
                } else {
                	NewX = GetRandomNumber(0, 2);
                	NewY = GetRandomNumber(0, 2);
                	if(NewX == 2)
                	{
                    		NewX = -1;
                	}
                	if(NewY == 2)
                	{
                    		NewY = -1;
                	}
                }
            	this->walk(NewX, NewY);

seedrand() seeds the random function to the system time, and this->walk adds on the x and y parameters to the current x and y variables.
Thanks.