UGH PROBLEMS!!!!

[kogamint]

I cannot get this simulation right. Can any advanced users help me debug this?
#include <GL/glut.h>
#include <vector>
#include <cmath>

struct Particle {
float x;
float y;
float r;
float vx;
float vy;
float m;
float color[3];
};

struct Line {
float x1;
float y1;
float x2;
float y2;
} line;

void timer(int = 0);
void display();
void mouse(int, int, int, int);
void mouseMotion(int, int);
void addParticle(float, float, bool = true, float = 0, float = 0);
void removeParticles();
void keyboard(unsigned char, int, int);

int Mx, My, WIN;
bool PRESSED_LEFT = false, PRESSED_RIGHT = false,
PRESSED_MIDDLE = false, SPEED_PARTICLES = false;

std::vector<Particle> particles;

int main(int argc, char **argv)
{
Particle p;
//initial centered Huge mass particle
p.x = 0;
p.y = 0;
p.vx = p.vy = 0;
p.m = 10000;
p.r = 10;
p.color[0] = 1;
p.color[1] = 1;
p.color[2] = 0;
particles.push_back(p);

glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(500, 500);
glutInitWindowPosition(50, 50);
WIN = glutCreateWindow("Gravity");

glClearColor(0, 0, 0, 1);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-250.0, 250.0, 250.0, -250.0, 0, 1);

glutDisplayFunc(display);
glutMouseFunc(mouse);
glutMotionFunc(mouseMotion);
glutKeyboardFunc(keyboard);
timer();

glutMainLoop();
return 0;
}

void timer(int)
{
display();
if(PRESSED_LEFT && !SPEED_PARTICLES)
{
addParticle(10, 3); //add tiny particle
PRESSED_LEFT = false;
}

if(PRESSED_RIGHT)
{
addParticle(10000, 10, 0); //add huge particle
PRESSED_RIGHT = false;
}

if(PRESSED_MIDDLE)
removeParticles(); //remove all particles

for(int i = 0; i < particles.size(); i++)
{
Particle &p = particles[i];
bool not_fall = true;
for(int j = 0; j < particles.size(); j++)
{
if(j == i || p.m >= 10000) // we consider the 10000 as infinit (big mass) so this particles won't move
continue;

const Particle &p1 = particles[j];

float d = sqrt((p1.x - p.x)*(p1.x - p.x) + (p1.y - p.y)*(p1.y - p.y));

if(d > p1.r)
{
p.vx += 0.03 * p1.m / (d*d) * (p1.x - p.x)/d; //f = ma => a = f/m
p.vy += 0.03 * p1.m / (d*d) * (p1.y - p.y)/d;
}
else
not_fall = false;
}

if(not_fall)
{
p.x += p.vx;
p.y += p.vy;
}
else
particles.erase(particles.begin()+i);
}

glutTimerFunc(1, timer, 0);
}

void display()
{
glClear(GL_COLOR_BUFFER_BIT);

//draw the drag line
glColor3f(0, 0, 1);
glBegin(GL_LINES);
glVertex2f(line.x1, line.y1);
glVertex2f(line.x2, line.y2);
glEnd();

//draw particles
for(int i = 0; i < particles.size(); i++)
{
Particle &p = particles[i];
glColor3f(p.color[0], p.color[1], p.color[2]);
glBegin(GL_POLYGON);
for(float a = 0; a < 2*M_PI; a+=0.2)
glVertex2f(p.r*cos(a) + p.x, p.r*sin(a) + p.y);
glEnd();
}

glFlush();
glutSwapBuffers();
}

void mouse(int button, int state, int x, int y)
{
//set the coordinates
Mx = x - 250;
My = y - 250;

//add speed particles by line draging
if(SPEED_PARTICLES)
{
if(line.x2 != 0 && line.y2 != 0 && state == GLUT_UP && PRESSED_LEFT)
addParticle(100, 5, 1, line.x1 - line.x2, line.y1 - line.y2); //add a speed particle
else
{
line.x1 = line.x2 = Mx;
line.y1 = line.y2 = My;
}
}

//check which button is pressed
if(button == GLUT_LEFT_BUTTON)
PRESSED_LEFT = state == GLUT_DOWN;
else if(button == GLUT_RIGHT_BUTTON)
PRESSED_RIGHT = state == GLUT_DOWN;
else if(button == GLUT_MIDDLE_BUTTON)
PRESSED_MIDDLE = state == GLUT_DOWN;
}

void mouseMotion(int x, int y)
{
Mx = x - 250;
My = y - 250;

//end of line with draging
if(SPEED_PARTICLES && PRESSED_LEFT)
{
line.x2 = Mx;
line.y2 = My;
}
}

void addParticle(float m, float r, bool randColor, float vx, float vy)
{
Particle p;
p.x = Mx;
p.y = My;
p.vx = vx / 30; // /30 in case it is a speed particle,
p.vy = vy / 30; // slow down the speed a little
p.m = m;
p.r = r;
if(randColor)
{
p.color[0] = rand()%200 / 200.0;
p.color[1] = rand()%200 / 200.0;
p.color[2] = rand()%200 / 200.0;
}
else // if is huge particle make it yellow
{
p.color[0] = 1;
p.color[1] = 1;
p.color[2] = 0;
}
particles.push_back(p);

if(line.x1 != 0)
line.x1 = line.x2 = line.y1 = line.y2 = 0;
}

void removeParticles()
{
for(int i = 0; i < particles.size(); i++)
particles.pop_back();
}

void keyboard(unsigned char key, int x, int y)
{
switch(key)
{
case 's':
SPEED_PARTICLES = !SPEED_PARTICLES;
break;
case 27:
removeParticles();
glutDestroyWindow(WIN);
exit(0);
break;
}
}

[Bdanielz]

post this in code tags. It is easier to read.
http://www.cplusplus.com/forum/articles/16853/

What error are you getting?
What are you expecting to happen?
What is happening instead?