Jeremy Visser

A word of warning: don’t read this post. You’ll regret it. It’s basically a convoluted regurgitation of my brain with regards to using linked lists in C. Here be dragons.

In C, creating variables, and storing values in them is quite easy. You just declare them as such:

int i;

And then perform whatever operations you want with them:

i = 2;
i = i * 2;
printf("%d", i); /* 4 */

There is also a cool thing called struct, which lets you create a big variable that contains lots of sub-variables. It works a bit like this:

typedef struct tagGameObject {
	int x;
	int y;
} GameObject;

Then, you can create ‘instances’ of it like this: (note the scare quotes, because C isn’t really object-oriented)

GameObject rocket;
GameObject monster;

rocket.x = 20;
rocket.y = 25;

monster.x = 300;
monster.y = 250;

printf("rocket is at (%d,%d)", rocket.x, rocket.y); // rocket is at (20,25)
printf("monster is at (%d,%d)", monster.x, monster.y); // monster is at (300,250)

Now, let’s just say I wanted to have 3 monsters. I could create three of them like this:

GameObject monster_1;
GameObject monster_2;
GameObject monster_3;

monster_1.x = 100; /* ...etc. */

However, that’s a bit tedious. What if I wanted 20 monsters? Surely I don’t declare each one individually. Nope — you can use arrays for that, which are pretty easy.

GameObject monsters[20];

monsters[0].x = 100;
monsters[1].x = 110;
monsters[2].x = 120; /* ...etc. */

But that has a problem. I’m stuck with 20 monsters all at the same time. Even if you are not using all monsters in the array, the memory is always allocated for each one. Sometimes that is what you want. Sometimes it is not. What if you wanted to be able to create and delete monsters at wish, and it didn’t matter how many you had at any one time?

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