A few questions about lite-C game development

function spot_init(SPOT* spot) 
{ 
  if (!spot) return; // prevent crash when an empty pointer is passed
  spot.x = 1; 
  spot.y = 1; 
}
...
SPOT myspot; // creates an uninitalized SPOT struct named "myspot"
...
spot_init(myspot); // passes a pointer to myspot

function vector_add2 (var* sum,var* v1,var* v2)
{
	//calculate the sum of two vectors
	sum[0] = v1[0] + v2[0];
	sum[1] = v1[1] + v2[1];
	sum[2] = v1[2] + v2[2];
}
var vector1[3] = { 1,2,3 };
var vector2[3] = { 4,5,6 };
var vector3[3];
//...
vector_add2 (vector3,vector1,vector2); //vector3 now contains 5,7,9

function vector_add2 (var* sum,var* v1,var* v2,ENTITY* ent,PARTICLE* p) ???
{
	//calculate the sum of two vectors
	sum[0] = v1[0] + v2[0];
	sum[1] = v1[1] + v2[1];
	sum[2] = v1[2] + v2[2];
}
var vector1[3] = { 1,2,3 };
var vector2[3] = { 4,5,6 };
var vector3[3];
//...
vector_add2 (vector3,vector1,vector2); //vector3 now contains 5,7,9

#define LOW_RES
...
#ifndef LOW_RES
  video_mode = 8; // 1024x768
#else
  video_mode = 6; // 640x480
#endif

//#define USE_PHYSX3

#ifdef USE_PHYSX3
	#include <ackphysx3.h>
	#else
	#include <ackphysx.h>
#endif

void create_physics_ent()
{
	ENTITY* ent_tmp=ent_create(CUBE_MDL,nullvector,NULL);
	
	#ifdef USE_PHYSX3
		pX3ent_settype(ent_tmp,PH_RIGID,PH_BOX);
		pX3ent_setdamping(ent_tmp,50,80);
		pX3ent_setskinwidth(ent_tmp,0);
		pX3ent_setiterations(ent_tmp,16);
		pX3ent_setfriction(ent_tmp,100);

		#else

		pXent_settype(ent_tmp,PH_RIGID,PH_BOX);
		pXent_setdamping(ent_tmp,50,80);
		pXent_setskinwidth(ent_tmp,0);
		pXent_setiterations(ent_tmp,16);
		pXent_setfriction(ent_tmp,100);
	#endif
}

function disconnect_event() 
{
  if (event_type == EVENT_DISCONNECT)
  {
    ptr_remove(me);
  }
}

action actor()
{
  ...
  my.emask |= ENABLE_DISCONNECT; // sensible for disconnects
  my.event = disconnect_event;
  ...
}

my.skill3 = 100;
my.skill[2] = 100;

str_cpy(name_str,my.string1);

function p_alphafade (PARTICLE *p)
{
	p.alpha -= p.skill_a*time_step;
	if (p.alpha <= 0) p.lifespan = 0;
}

function p_trace (PARTICLE *p)
{
	set (p,BRIGHT | TRANSLUCENT | BEAM);
	p.size = 2;
	p.skill_a = 1; //fade factor
	p.event = p_alphafade;
}

//entity that runs in circles and leaves a vapor trail
action tracer ()
{
	var dist = 0,radius = 10,sign = 1;
	VECTOR last_pos;
	while (1)
	{
		vec_set (last_pos,my.x);
		dist += 30*time_step;
		radius += sign*random(3)*time_step; //change radius randomly
		if (radius > 150) sign = -1;
		else if (radius < 30) sign = 1;
		my.x = radius*sin(dist);
		my.y = radius*cos(dist);
		effect (p_trace,1,my.x,vec_sub(last_pos,my.x));
		wait (1);
	}
}

function main ()
{
	vec_set (sky_color, vector (50,1,1)); //dark blue
	level_load (NULL);
	video_window (NULL, NULL, 0, "Vapor trail demo");
	vec_set (camera.x, vector (-250,0,50));
	vec_set (camera.pan, vector (0, -15,0));
	ent_create (NULL, vector (0,0,0),tracer);
}

#include <acknex.h>

function p_alphafade (PARTICLE *p)
{
	p.alpha -= p.skill_a*time_step;
	if (p.alpha <= 0) p.lifespan = 0;
}

function p_trace (PARTICLE *p)
{
	set (p,BRIGHT | TRANSLUCENT | BEAM);
	p.size = 2;
	p.skill_a = 1; //fade factor
	p.event = p_alphafade;
}

//entity that runs in circles and leaves a vapor trail
action tracer ()
{
	var dist = 0,radius = 10,sign = 1;
	VECTOR last_pos;
	while (1)
	{
		vec_set (last_pos,my.x);
		dist += 30*time_step;
		radius += sign*random(3)*time_step; //change radius randomly
		if (radius > 150) sign = -1;
		else if (radius < 30) sign = 1;
		my.x = radius*sin(dist);
		my.y = radius*cos(dist);
		effect (p_trace,1,my.x,vec_sub(last_pos,my.x));
		wait (1);
	}
}

function main ()
{
	vec_set (sky_color, vector (50,1,1)); //dark blue
	level_load (NULL);
	video_window (NULL, NULL, 0, "Vapor trail demo");
	vec_set (camera.x, vector (-250,0,50));
	vec_set (camera.pan, vector (0, -15,0));
	ent_create (NULL, vector (0,0,0),tracer);
}