code:

void CParticleSystem::verlet()
{
	for(int i = 0; i < m_vParticles.size(); i++)
	{
		SParticle* p = m_vParticles[i];
		Vector2 temp = m_vParticles[i]->position;
		p->position += p->position - p->oldPosition + p->forces * (m_timeStep * m_timeStep);
		p->oldPosition = temp;
	}
}

void CParticleSystem::satisfyConstraints()
{
	for(int iterations = 0; iterations < NUM_ITERATIONS; iterations++)
	{
		for(int i = 0; i < m_vParticles.size(); i++)
		{
			m_vParticles[i]->position = 
                Vector2::vmin(Vector2::vmax(m_vParticles[i]->position, Vector2(0.0f, 0.0f)), Vector2(1000.0f, 1000.0f));
		}

		for(int i = 0; i < m_vConstraints.size(); i++)
		{
			Vector2 &x1 = m_vConstraints[i]->pParticleA->position;
			Vector2 &x2 = m_vConstraints[i]->pParticleB->position;
			Vector2 delta = x2 - x1;
			float rLength = m_vConstraints[i]->restLength;
			delta *= (rLength * rLength) / ((Vector2::dot(delta,delta)) + (rLength * rLength)) - 0.5;
			x1 -= delta;
			x2 += delta;
		}
	}
}