N00bish function wont work with class thingy

[Zer0XoL]

Ok, hello
I thought i would make a simple text game before continuing with SDL
And well, i have problems xD.
Now, everytime i try to attack Slagor hes HP is always "reset"(not good), BUT i can decrese his HP in the main function.(but i want it to work in the attack function)
And here is the WHOLE code:) :

Code: Select all

#include <iostream>
using namespace std;
class Player
{
      private:
              bool IsAlive;
              int exp, hp, mp, power;
      public:
             char name;
             int GetHP()
             {
                   return hp;
                   }
              void AddHP(int h)
              {
                   hp += h;
                   }
              
              
              void Die(){
                   IsAlive = false;
                   }
              void Attack(Player e)
              {
                   e.SubHP(exp*power);
                   cout << "You attacked " << "another player" << " with " << exp*power << " damage!\n";
                   cout << "Enemy hp left: " << e.GetHP() << "!\n";
                   }
                   
              void Default()
              {
                   IsAlive = true;
                   exp = 1;
                   hp = 100;
                   power = 1;
                   mp = 50;
                   }
              void SubHP(int p)
              {
                   hp = hp - p;
                   }
                   
                   
                   
};
int main()
{   
    cout << "Welcome!\n\n\n";
    Player Zer0XoL;
    Zer0XoL.Default();
    Player Slagor;
    Slagor.Default();
    Zer0XoL.Attack(Slagor);
    Zer0XoL.Attack(Slagor);
    Zer0XoL.Attack(Slagor);
    Zer0XoL.Attack(Slagor);
    Slagor.Attack(Zer0XoL);
    Zer0XoL.Attack(Slagor);
    Zer0XoL.Attack(Slagor);
    Slagor.SubHP(66);
    cout << "New hp:" << Slagor.GetHP() <<endl;
    Zer0XoL.Attack(Slagor);
    Zer0XoL.Attack(Slagor);
    Zer0XoL.Attack(Slagor);
    Slagor.SubHP(-1);
    cout << "New hp: " << Slagor.GetHP() <<endl;
    Zer0XoL.Attack(Slagor);
    Zer0XoL.Attack(Slagor);
    Zer0XoL.Attack(Slagor);
    cin.get();
    cin.get();
}

If you have thoughts about that i do something wrong in anyway, just tell me and ill learn more, thank you.

*Edit:
this is the output of the program(im using Dev-Cpp)
:

Code: Select all

Welcome!


You attacked another player with 1 damage!
Enemy hp left: 99!
You attacked another player with 1 damage!
Enemy hp left: 99!
You attacked another player with 1 damage!
Enemy hp left: 99!
You attacked another player with 1 damage!
Enemy hp left: 99!
You attacked another player with 1 damage!
Enemy hp left: 99!
You attacked another player with 1 damage!
Enemy hp left: 99!
You attacked another player with 1 damage!
Enemy hp left: 99!
New hp:34
You attacked another player with 1 damage!
Enemy hp left: 33!
You attacked another player with 1 damage!
Enemy hp left: 33!
You attacked another player with 1 damage!
Enemy hp left: 33!
New hp: 35
You attacked another player with 1 damage!
Enemy hp left: 34!
You attacked another player with 1 damage!
Enemy hp left: 34!
You attacked another player with 1 damage!
Enemy hp left: 34!

As you can see the hp always "resets". =/

[dani93]

When you call the function

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void Attack(Player e)

the object form main is copied to the object called "e". "e" is destroyed after the execution leaves the scope. So you don't change the correct object. To use the object from main, you can pass a reference (or a pointer) to it.

Code: Select all

void Attack(Player& e)

Do you understand what I mean?

There are some other things in your code that aren't... I mean they are not wrong... but also not nice
For the function "Default" you could use a constructor. The definition of the class and the implementations of the methods should be in seperate files.

[Zer0XoL]

When you call the function

Code: Select all

void Attack(Player e)

the object form main is copied to the object called "e". "e" is destroyed after the execution leaves the scope. So you don't change the correct object. To use the object from main, you can pass a reference (or a pointer) to it.

Code: Select all

void Attack(Player& e)

Do you understand what I mean?

There are some other things in your code that aren't... I mean they are not wrong... but also not nice
For the function "Default" you could use a constructor. The definition of the class and the implementations of the methods should be in seperate files.

Thank you, i couldn´t define the variables in the class so i made a function.. how does constructors work, or what are they?(im reading a swedish c++ book, i SHOULD know )
Also im planning to splitt it into files, but not yet.
and yes i understand what you mean with pointers but i didnt rely try it.
Thank you, a lot

[Ewan]

In your Attack function, it's a copy of the instance of Player that's being passed as an argument, not the actual instance. It's like copying a file and putting it into a different folder then modifying the contents of the new file, when really you want to change the data in the original.

You'll need to do this instead:

Change your Attack function to

Code: Select all

     
void Attack(Player *e)
{
       e->SubHP(exp*power);
       cout << "You attacked " << "another player" << " with " << exp*power << " damage!\n";
       cout << "Enemy hp left: " << e->GetHP() << "!\n";
}

and every time you use Attack you will need to do it like this:

Code: Select all

Zer0XoL.Attack(&Slagor);

http://www.cplusplus.com/doc/tutorial/pointers/

Hope this helped

Ewan

EDIT: Hehe you beat me to it

EDIT 2: Dani93's solution is better lol, use his

[Zer0XoL]

In your Attack function, it's a copy of the instance of Player that's being passed as an argument, not the actual instance. It's like copying a file and putting it into a different folder then modifying the contents of the new file, when really you want to change the data in the original.

You'll need to do this instead:

Change your Attack function to

Code: Select all

     
void Attack(Player *e)
{
       e->SubHP(exp*power);
       cout << "You attacked " << "another player" << " with " << exp*power << " damage!\n";
       cout << "Enemy hp left: " << e->GetHP() << "!\n";
}

and every time you use Attack you will need to do it like this:

Code: Select all

Zer0XoL.Attack(&Slagor);

http://www.cplusplus.com/doc/tutorial/pointers/

Hope this helped

Ewan

EDIT: Hehe you beat me to it

EDIT 2: Dani93's solution is better lol, use his

Hey thanks, this is a rely great forum (thumbs up)

[dani93]

how does constructors work, or what are they?

A constructor is automatically called when you create an object. It has the same name as the class.
Your constructor could look like that:

Code: Select all

Player ()                // same name as class
{

                   IsAlive = true;
                   exp = 1;
                   hp = 100;
                   power = 1;
                   mp = 50;

}

So you don't need to call "Default" everytime you create an object.

You'll need to do this instead:

Change your Attack function to
[...]

Yes, that is the pointer-version
But I like the comparism to files.

EDIT: Hehe you beat me to it

EDIT 2: Dani93's solution is better lol, use his

I'm not really a C++ pro. Why should a reference be better than a pointer? OK, you don't need to care about if you use values or adresses

[Zer0XoL]

how does constructors work, or what are they?

A constructor is automatically called when you create an object. It has the same name as the class.
Your constructor could look like that:

Code: Select all

Player ()                // same name as class
{

                   IsAlive = true;
                   exp = 1;
                   hp = 100;
                   power = 1;
                   mp = 50;

}

So you don't need to call "Default" everytime you create an object.

I'm not really a C++ pro. Why should a reference be better than a pointer? OK, you don't need to care about if you use values or adresses

Ooh, that is really usefull feature!
I can´t thank you more

[Ewan]

EDIT 2: Dani93's solution is better lol, use his

I'm not really a C++ pro. Why should a reference be better than a pointer? OK, you don't need to care about if you use values or adresses

Well, mainly because with pointers you have to use -> to access member functions, and when passing the argument you have to put &Slagor or whatever instead of just Slagor. Not that references are always better, but this time they just made more sense.

Btw, when I said "do this instead" I was saying instead of his original code - I hadn't seen your reply.

[dani93]

Ooh, that is really usefull feature!
I can´t thank you more

You're welcome

Well, mainly because with pointers you have to use -> to access member functions, and when passing the argument you have to put &Slagor or whatever instead of just Slagor. Not that references are always better, but this time they just made more sense.

True

Btw, when I said "do this instead" I was saying instead of his original code - I hadn't seen your reply.

Yeah, I know, cause saw your EDIT (and even quoted it)

[MarauderIIC]

You can reseat a pointer, ie, make it point to something else. You can also delete what it points to. If you shouldn't be able to delete what the pointer points to, you should use a reference.

[Zer0XoL]

You can reseat a pointer, ie, make it point to something else. You can also delete what it points to. If you shouldn't be able to delete what the pointer points to, you should use a reference.

Ill use a reference

[newbie1234]

void SubHP(int p)
{
hp = hp - p;
}

And offcourse, you could use hp -= p;

[dandymcgee]

And offcourse, you could use hp -= p;

Dude last post was Tue May 05, 2009. Unless you have something you feel would be vital to the archival of 4 month old topic, please at least make an effort to resist the urge to reply to it. Thanks.

[newbie1234]

It was lag.