Thread: modifying a value in an object?

I made the following code as practice with classes and objects. However, when I try to modify the value of int hp inside the takedam function, it doesn't change anything outside the function. What is the best/most efficient way to change this value? I'm willing to read up on stuff, so if you point me in the right direction I'll try to figure it out.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

class zergling
{
	char name[20];
	int hp;
	int basedamage;
	public:
	zergling(int starthp, int dmg, char *label); //constructor declaration
	~zergling() {}; //destructor declaration and definition.
	
	int attack(int damage, zergling target);
	int takedam(int dam);
};

zergling::zergling(int starthp, int basedmg, char *label) //definition of the constructor.
{
	strcpy(name,label);
	hp=starthp;
	basedamage=basedmg;
}

int zergling::attack(int damage, zergling target)
{
	int dmgtot=rand()%3+target.basedamage;
	printf("\nabout to inflict %d damage on a zergling, named %s\n",dmgtot,target.name);
	target.takedam(dmgtot);
}

int zergling::takedam(int dam)
{
	hp-=dam;
	printf("\na zergling named %s has taken %d dam, and now has %d hp left.\n",name,dam,hp);
}


int main()
{
	srand(time(NULL)); //starting the RNG base.
	printf("\nThis is a game of chance.\n");
	char name1[20];
	char name2[20];
	printf("Enter the name of player 1: ");
	scanf("%s",name1);
	printf("Enter the name of player 2: ");
	scanf("%s",name2);
	
	zergling z1(35,5,name1);
	zergling z2(35,5,name2);
	
	printf("\nLet the battle begin!\n\n");
	
	while (1)
	{
	z1.attack(3,z2);
	sleep(1);
	//z2.attack(3,z1);
	//sleep(1);
	}
	
}

Try "pass by reference".

I've used pointers before, so that makes a lot of sense. However, this was (probably) the closest I got to doing it right:

Code:

int zergling::takedam(int dam)
{
	int *temp=&hp;
	*temp=hp-dam;
	printf("\na zergling named %s has taken %d dam, and now has %d hp left.\n",name,dam,hp);
}

I have no idea why that won't work. Any tips?

Problem is

Code:

int zergling::attack(int damage, zergling target)
{
	int dmgtot=rand()%3+target.basedamage;
	printf("\nabout to inflict %d damage on a zergling, named %s\n",dmgtot,target.name);
	target.takedam(dmgtot);
}

"target" is passed by value.

To take a wild guess, this should work -

Code:

int zergling::attack(int damage, zergling &target)
{
	int dmgtot=rand()%3+target.basedamage;
	printf("\nabout to inflict %d damage on a zergling, named %s\n",dmgtot,target.name);
	target.takedam(dmgtot);
}

And this is C++, pointers != references.

I think what he meant is "this" zergling attacks the "target" zergling.

"damage" is unused, though, and doesn't really make sense here.

Originally Posted by laserlight

So, at some later point, you may want to have the damage inflicted depend on the attacker?

Exactly. Planning on implementing hydralisks and such, again just as practice so I've got some experience using these.

By the way, on a completely different note, is there some sort of documentation I could read up on on why you would ever want to make something private? I don't see why you would need to hide something from your own code minus code injection...

Thank you!