C++ changing instance variables [closed] - c++

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I am trying to write a program to calculate an n-body problem. I have run into a problem trying to change my code so it would be easily adaptable for any number of bodies. There seems to be a problem with the function corr(), the changes made to some variables of the instances of the class particle in this function seem to get lost after the function corr() has been used. How do i solve this problem?
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <fstream>
#define h 1000.0
#define G 6.67384*pow(10.0,-11)
using namespace std;
class particle{
public:
double kx1,kx2,kx3,kx4, kv1, kv2, kv3, kv4;
double ky1, ky2, ky3, ky4, kvy1, kvy2, kvy3, kvy4;
double x,y,vx,vy,m;
double dist(particle aap){
double dx = x - aap.x;
double dy = y - aap.y;
return sqrt(pow(dx,2.0)+pow(dy,2.0));
}
double g(double x1, double y1,particle aap){
return G*aap.m*(aap.x-x1)/pow(dist(aap),3.0);
}
double p(double x1, double y1, particle aap){
return G*aap.m*(aap.y-y1)/pow(dist(aap),3.0);
}
void update(){ //zet het object 1 stap vooruit
x = x + (1/6.0)*(kx1+2*kx2+2*kx3+kx4);
vx = vx + (1/6.0)*(kv1+2*kv2+2*kv3+kv4);
y = y + (1/6.0)*(ky1+2*ky2+2*ky3+ky4);
vy = vy + (1/6.0)*(kvy1+2*kvy2+2*kvy3+kvy4);
}
void create(double x1, double y1, double vx1, double vy1, double m1){
x = x1;
y = y1;
vx = vx1;
vy = vy1;
m =m1;
}
bool operator ==(particle &other){
if(x == other.x && y == other.y && vx == other.vx && vy == other.vy){
return true;
}
}
};
particle zon, maan, aarde;
void set(){
zon.create(1, 1, -2, 1, 2*pow(10.0,30));
aarde.create(1.5*pow(10.0,11), 0, 2, 29780, 6*pow(10.0,24));
maan.create(aarde.x + 1, aarde .y + 3.844399*pow(10.0,8), aarde.vx + -1022.0, aarde.vy + 1, 7.3347*pow(10.0,22));
}
double xforce(double x1, double y1, particle aap){ //kracht in de x-richting
particle bodies[] = {zon, aarde, maan};
double fx;
for (int i = 0; i < 3; i++){
if (bodies[i].x == aap.x && bodies[i].y == aap.y && bodies[i].vx == aap.vx && bodies[i].vy == aap.vy ){;}
else{
fx += aap.g(x1,y1,bodies[i]);
}
}
return fx;
}
double yforce(double x1, double y1, particle aap){ //kracht in de y-richting
particle bodies[] = {zon, aarde, maan};
double fy;
for (int i = 0; i <= 3; i++){
if (bodies[i].x == aap.x && bodies[i].y == aap.y && bodies[i].vx == aap.vx && bodies[i].vy == aap.vy) {;}
else{
fy += aap.p(x1,y1,bodies[i]);
}
}
return fy;
}
void corr(particle body){
body.kx1 = h*body.vx;
body.kv1 = h*xforce(body.x, body.y, body);
body.ky1 = h*body.vy;
body.kvy1 =h*yforce(body.x, body.y, body);
body.kx2 = h*(body.vx + 0.5*body.kv1);
body.kv2 = h*xforce(body.x + 0.5*body.kx1, body.y + 0.5*body.ky1, body);
body.ky2 = h*(body.vy + 0.5*body.kvy1);
body.kvy2 = h*yforce(body.x + 0.5*body.kx1, body.y + 0.5*body.ky1, body);
body.kx3 = h*(body.vx+ 0.5*body.kv2);
body.kv3 = h*xforce(body.x + 0.5*body.kx2, body.y + 0.5*body.ky2, body);
body.ky3 = h*(body.vy+ 0.5*body.kvy2);
body.kvy3 = h*yforce(body.x + 0.5*body.kx2, body.y + 0.5*body.ky2,body);
body.kx4 = h*(body.vx+body.kv3);
body.kv4 = h*xforce(body.x+ body.kx3, body.y + body.ky3, body);
body.ky4 = h*(body.vy + body.kvy3);
body.kvy4 = h*yforce(body.x + body.kx3, body.y + body.ky3, body);
}
void bereken(){
set();
ofstream file;
file.open("3body.txt");
for(int i =0; i <=30000; i++){
corr(maan);
corr(zon);
corr(aarde);
zon.update();
aarde.update();
maan.update();
file << i*h <<" "<< zon.x << " "<< zon.y << " "<< zon.vx<< " "<< zon.vy <<" "<< aarde.x << " " << aarde.y <<" "<< aarde.vx <<" " << aarde.vy <<" "<< maan.x<<" "<<maan.y<<"\n";
}
file.close();
}
int main()
{
set();
bereken();
system("pause");
return 0;
}

Answer 1

Just use references:
void corr(particle& body)
The same fix has to be applied in other places. What you currently have is a code that COPIES your object, does some calculations on it and then just deletes this temporary object... By using reference (&) you effectively "share" the object between the caller and callee.
In your class methods you should also use references for passing this object, but this time for efficiency reasons - it's simple to pass reference (usually the same as pointer), but copying this huge object takes time.

Answer 2

The suggestion made by Freddie Chopin worked and fixed the function corr(). Now however i came across the fact that the functions xforce() and yforce() don't work properly. They are supposed to return the total force on a certain particle, which they do in the first step, but after that they seem to be returning wrong values. Anyone has an idea why that happens?