Problem with array of class objects leads to crash - c++

Question

So I am making a textbased RPG and I wanted to have multiple enemy encounter at once. So I modified my function that determines whether an object of the class Monster, to fill in the Monster(s) into an array of the class monster and set the objects bool to true, as you can see here:
Monster * Map::checkRandomEncounter()
{
Monster* monster = new Monster[3];
for (int i = 0; i < 3; i++)
{
int roll = Random(0, 20);
if (roll <= 5)
{
//No encounter
return 0;
}
else if (roll > 6 && roll < 10)
{
monster[i] = Monster();
monster[i].giveID("Orc", 10, 8, 200, 100, 1, "Short Sword", 2, 7);
monster[i].isFilled();
std::cout << "You encounter an Orc!" << std::endl;
std::cout << "Prepare for battle!" << std::endl;
std::cout << std::endl;
}
else if (roll >= 11 && roll <= 15)
{
monster[i] = Monster();
monster[i].giveID("Goblin", 6, 6, 100, 75, 0, "Dagger", 1, 5);
monster[i].isFilled();
std::cout << "You encounter a Goblin!" << std::endl;
std::cout << "Prepare for battle!" << std::endl;
std::cout << std::endl;
}
else if (roll >= 16 && roll <= 19)
{
monster[i] = Monster();
monster[i].giveID("Ogre", 20, 12, 500, 200, 2, "Club", 3, 8);
monster[i].isFilled();
std::cout << "You encounter an Ogre!" << std::endl;
std::cout << "Prepare for battle!" << std::endl;
std::cout << std::endl;
}
else if (roll == 20)
{
monster[i] = Monster();
monster[i].giveID("Orc Lord",
25,
15,
2000,
1000,
5,
"Two Handed Sword",
5,
20);
monster[i].isFilled();
std::cout << "You encounter an Orc Lord!" << std::endl;
std::cout << "Prepare for battle!" << std::endl;
std::cout << std::endl;
}
}
return monster;
}
The function above will be called in my main function, which looks like this:
int main()
{
srand(time(0));
Map gameMap;
Player mainPlayer;
mainPlayer.createClass();
//Beginn adventure
bool done = false;
while (done == false)
{
// Each Loop Cycle outputs player pos and selection menu
gameMap.printPlayerPos();
int selection = 1;
std::cout << "1) Move 2) Rest 3) View Stats 4) Quit: ";
std::cin >> selection;
Monster* monster = 0;
switch (selection)
{
case 1: // Move the player
gameMap.movePlayer();
if (gameMap.getPlayerXPos() == 2
&& gameMap.getPlayerYPos() == 3)
{
std::cout << "You see a store nearby !" << std::endl;
}
if (gameMap.getPlayerXPos() == 2
&& gameMap.getPlayerYPos() == 4)
{
Store store;
store.enter();
store.showInventory(mainPlayer);
}
//Check for a random encounter
//returns a null pointer if no encounter happened
monster = gameMap.checkRandomEncounter();
//'monster' not null, start battle script
if (monster != 0)
{
//Loop until a break statement
for (int i = 0; i < 3; i++)
{
//Display Hitpoints
mainPlayer.displayHitPoints();
monster[i].displayHitPoints();
std::cout << std::endl;
//Players turn to attack first
**bool runAway = mainPlayer.attack(monster, mainPlayer);** // Crash happening in this area
if (runAway) // Player flees
{
break;
}
if (monster[i].isDead())
{
mainPlayer.victory(monster->getXPReward(),
monster->getGoldReward());
mainPlayer.levelUp(mainPlayer);
}
break;
//Monster attacks
monster[i].attack(mainPlayer);
if (mainPlayer.isDead())
{
mainPlayer.gameOver();
done = true;
break;
}
}
//Pointer to Monster must destroy created instance of Monster
//to make sure that there is no Memory leak
}
delete monster;
monster = 0;
break;
case 2: // resting
mainPlayer.rest();
monster = gameMap.checkRandomEncounter();
//'monster' not null, start battle script
monster = gameMap.checkRandomEncounter();
//'monster' not null, start battle script
if (monster != 0)
{
//Loop until a break statement
for (int i = 0; i < 3; i++)
{
//Display Hitpoints
mainPlayer.displayHitPoints();
monster[i].displayHitPoints();
std::cout << std::endl;
//Players turn to attack first
bool runAway = mainPlayer.attack(monster, mainPlayer);
if (runAway) // Player flees
{
break;
}
if (monster[i].isDead())
{
mainPlayer.victory(monster->getXPReward(),
monster->getGoldReward());
mainPlayer.levelUp(mainPlayer);
}
break;
//Monster attacks
monster[i].attack(mainPlayer);
if (mainPlayer.isDead())
{
mainPlayer.gameOver();
done = true;
break;
}
}
//Pointer to Monster must destroy created instance of Monster
//to make sure that there is no Memory leak
}
delete monster;
monster = 0;
break;
case 3: // viewing stats
mainPlayer.viewStats();
break;
case 4: // quitting
done = true;
break;
}
}
return 0;
}
and finally the last puzzle piece, the function where the player attacks the Monster(s):
bool Player::attack(Monster Monster[], Player& Player)
{
int ArmorBefore = 0;
int Roll = 0;
int selection = 1;
int i;
if (Monster[0].isFilled() == true)
{
i = 0;
}
else if (Monster[1].isFilled() == true)
{
i = 1;
}
else if (Monster[2].isFilled() == true)
{
i = 2;
}
if (Monster[i].isFilled() == true)
{
std::cout << "1) Attack 2) Run 3) Cast Spell 4) Use Item: ";
std::cin >> selection;
std::cout << std::endl;
switch (selection)
{
case 1: // Player fights
std::cout << " You attack an " << Monster[i].getName()
<< " with a " << mWeapon.mName << std::endl;
if (Random(0, 20) < mAccuracy) // Player hits Monster
{
int damage = Random(mWeapon.mDamageRange);
int totalDamage = damage - Monster[i].getArmor();
if (totalDamage <= 0) // Armor is equal or higher than player atk
{
std::cout << "Your attack failed to penetrate "
<< Monster[i].getName() << "'s armor !"
<< std::endl;
return false;
}
else // Attack is higher than Monsters armor
{
std::cout << "You hit " << Monster[i].getName()
<< " for " << totalDamage << " damage !"
<< std::endl;
// Subtract dmg from Monsters hp
Monster[i].takeDamage(totalDamage);
return false;
}
}
else // Player Misses
{
std::cout << "You miss !" << std::endl;
}
std::cout << std::endl;
return false;
break;
case 2: // Player runs with a 25% chance
Roll = Random(1, 4);
if (Roll == 1) // Success
{
std::cout << "You run away !" << std::endl;
return true; // <- Return out of the function
}
else
{
std::cout << "You failed to escape !" << std::endl;
return false;
}
case 3: // Casting Spell
{
int SpellSelect;
// Spells for the Fighter
if (Player.mClassName == "Fighter")
{
std::cout << std::endl;
std::cout << "1) Shield 2) Mighty Blow: ";
std::cin >> SpellSelect;
if (SpellSelect == 1)
{
if (Player.mMagicPoints >= 10) // checks for player mana
{
std::cout << "You cast a mighty shield!"
<< std::endl;
ArmorBefore = Player.mArmor;
Player.shield(Player);
Player.mMagicPoints -= 10;
}
else
{
std::cout << "Not enough Mana" << std::endl;
break;
}
}
else
{
if (Player.mMagicPoints >= 5) // casting Mighty Blow
{
int damage = Random(mMightyBlow.mDamageRange);
std::cout
<< "You strike with all your might ! and Deal "
<< damage << " damage !" << std::endl;
Monster[i].takeDamage(damage);
Player.mMagicPoints -= 5;
return false;
}
else
{
std::cout << "Not enough Mana" << std::endl;
return false;
}
}
}
//Spells for the Wizard
else if (Player.mClassName == "Wizard")
{
std::cout << "1) Fireball";
std::cin >> SpellSelect;
if (Player.mMagicPoints >= 45)
{
int damage = Random(mFireball.mDamageRange);
std::cout << "You cast a Fireball and deal " << damage
<< " damage !" << std::endl;
Monster[i].takeDamage(damage);
Player.mMagicPoints -= 45;
return false;
}
else
{
std::cout << "Not enough Mana" << std::endl;
return false;
}
}
// Spells for the Cleric
else if (Player.mClassName == "Cleric")
{
std::cout << "1) Magic Missile";
std::cin >> SpellSelect;
if (Player.mMagicPoints >= 35)
{
int damage = Random(mMagicMissile.mDamageRange);
std::cout << "You cast a Magic Missile and deal "
<< damage << " damage !" << std::endl;
Monster[i].takeDamage(damage);
Player.mMagicPoints -= 35;
}
else
{
std::cout << "Not enough Mana" << std::endl;
return false;
}
}
}
case 4: // using Item
int invSlot;
std::cout << "1) HP Potion: ";
std::cin >> invSlot;
if (invSlot == 1) // Potion slot
{
if (mHPot.mAmount.size() > 0)
{
std::cout << "You used a Potion and healed for 5 HP !"
<< std::endl;
int currentSize = mHPot.mAmount.size();
mHPot.mAmount.resize(currentSize - 1);
Player.mHitPoints += 5;
if (Player.mHitPoints > Player.mMaxHitPoints)
{
Player.mHitPoints = Player.mMaxHitPoints;
}
return false;
}
else
{
std::cout << "You have no Potions!" << std::endl;
return false;
}
}
else // wrong slot
{
std::cout << "No Item found!" << std::endl;
return false;
}
}
// Clearing stat boosts
if (Player.shield(Player) == true)
{
Player.mArmor = ArmorBefore;
}
}
return false;
}
When I run the game, I sometimes have the problem, that after filling in a Monster in a slot of the array, no battle will be triggered. And if a battle will be triggered, I get a crash with an error report every time, which says:
_CrtlValidHeadPointer(block)
I guess that something with my pointer is not functioning well.... but since I am a beginner I am pretty much stuck. I would be very grateful for some enlightenment :)

Answer 1

This place can potentially call undefined behavior and crash:
int i;
if (Monster[0].isFilled() == true)
{
i = 0;
}
else if (Monster[1].isFilled() == true)
{
i = 1;
}
else if (Monster[2].isFilled() == true)
{
i = 2;
}
/*else // one of solutions
break;*/
//"i" can be unset! and can have any value from INT_MIN to INT_MAX!
if (Monster[i].isFilled() == true) //potentially index over array
{
Also there are memory leaks and undefined behavior with memory management:
Monster* monster = new Monster[3];
...
delete monster
must be delete [] monster
but it is recommended to use smart pointers, vector, array, etc, for memory management