Processing - The variable 'i' does not exist? - processing

Question

I`ve tried finding a similar error to mine to avoid asking a already repeated question but I cannot find anything. I apologise for the code being quite long. If somebody could explain to me what I am doing wrong I would greatly appreciate it. Thanks in advance.
// Physical Constants
float g=-9.81; // Gravity
float k=0.0; // Friction const (Try 0.02)
float m=0.25; // Mass kg
float dt=0.01; // Time step 10ms
// Boundary (starting) conditions
float vy=0; // Initial vertical velocity
float y=0.9; // Initial vertical position
float x=0; // Initial horizontal position
float vx=0.8; // Initial horizontal velocity
float t=0; // Initial time
Ball [] b;
void setup()
{
b=new Ball[50];
for(int i=0;i<50;i++)
{
b[i]=new Ball();
}
size(500, 500);
}
void draw()
{
background(255);
for(int i=0;i<50;i++)
{
b[i].advance();
b[i].draw_ball();
}
}
int Collision(int j,Ball b[])
{
int res=-1;
for(int i=0;i<50;i++)
{
if (i!=j)
{
float sep=sqrt(pow(b[i].x-b[j].x,2)+pow(b[i].y-b[j].y,2));
float rads=b[i].radius+b[j].radius;
if(sep<rads){ res=i;}
}
}
return(res);
}
class Ball
{
color c;
float radius;
float vy;
float y;
float x;
float vx;
float t;
Ball()
{
y=random(0.1,0.9);
vy=random(-1,1);
x=random(0.1,0.9);
vx=random(-1,1);
c=color(random(255),random(255), random(255));
radius = 0.01+random(0.04);
t=0;
}
void advance()
{
vy=vy+(g-((k/m)*vy))*dt;
y=y+(vy*dt);
vx=vx+(-((k/m)*vx))*dt;
x=x+(vx*dt);
t=t+dt;
if (y<=0) {vy=-vy; y=y+(vy*dt);}
if (x<=0) {vx=-vx; x=x+(vx*dt);}
if (x>=1) {vx=-vx; x=x+(vx*dt);}
}
{
b[i].advance();
int r=Collision(i,b); // Check if ball i collides with any balls in array b
if(r!=-1) // -1 means no collision, r is index that identifies ball in b
{
float nvxj = (b[i].vx * (b[i].radius - b[r].radius) + (2 * b[r].radius * b[r].vx)) /
(b[i].radius + b[r].radius);
float nvyj = (b[i].vy * (b[i].radius - b[r].radius) + (2 * b[r].radius * b[r].vy)) /
(b[i].radius + b[r].radius);
float nvxr = (b[r].vx * (b[r].radius - b[i].radius) + (2 * b[i].radius * b[i].vx)) /
(b[i].radius + b[r].radius);
float nvyr = (b[r].vy * (b[r].radius - b[i].radius) + (2 * b[i].radius * b[i].vy)) /
(b[i].radius + b[r].radius);
b[i].vx=nvxj;
b[i].vy=nvyj;
b[r].vx=nvxr;
b[r].vy=nvyr;
}
b[i].draw_ball();
void draw_ball()
{
float sx=map(x,0,1,0,width);
float sy=map(y,0,1,height-1,0);
float rx=map(radius,0,1,0,width);
float ry=map(radius,0,1,0,height);
fill(c);
ellipse(sx,sy,2*rx,2*ry);
}
}

Answer 1

You'll have better luck if you fix your indentation so you can better match up { } curly brackets.
You've got an advance() function, but then right after that function ends (find the matching closing curly bracket), you've got this disconnected snippet of code:
{
b[i].advance();
int r=Collision(i, b); // Check if ball i collides with any balls in array b
if (r!=-1) // -1 means no collision, r is index that identifies ball in b
{
float nvxj = (b[i].vx * (b[i].radius - b[r].radius) + (2 * b[r].radius * b[r].vx)) /
(b[i].radius + b[r].radius);
float nvyj = (b[i].vy * (b[i].radius - b[r].radius) + (2 * b[r].radius * b[r].vy)) /
(b[i].radius + b[r].radius);
float nvxr = (b[r].vx * (b[r].radius - b[i].radius) + (2 * b[i].radius * b[i].vx)) /
(b[i].radius + b[r].radius);
float nvyr = (b[r].vy * (b[r].radius - b[i].radius) + (2 * b[i].radius * b[i].vy)) /
(b[i].radius + b[r].radius);
b[i].vx=nvxj;
b[i].vy=nvyj;
b[r].vx=nvxr;
b[r].vy=nvyr;
}
b[i].draw_ball();
void draw_ball()
{
float sx=map(x, 0, 1, 0, width);
float sy=map(y, 0, 1, height-1, 0);
float rx=map(radius, 0, 1, 0, width);
float ry=map(radius, 0, 1, 0, height);
fill(c);
ellipse(sx, sy, 2*rx, 2*ry);
}
}
There's a lot going on here. It's not a syntax error to have a block of code inside { } curly brackets like this, but I'm not sure what you're expecting this code to do, or when you expect it to run. But your error is caused by the fact that you're using an i variable in this code that you haven't defined.
It is a syntax error to define a function inside { } curly brackets like this though.
To fix your problem, you need to take a step back and really think about where this section of code belongs.