Object is erasing consecutive variable change

I am creating a project where for now I just want it to move a particle on a graphic window(SFML lib).
I look into creatinng multiple objects to interact with each other. So, i made a tick function that triggers all object’s tick function to handle collision, movement ect…
My problem is that each time I trigger my tick function, the position is adding to itself from the initial value I put in the constructor and not the already updated one causing the particle to not move at all.
I would apreciate any piece of advice or solutions !

#include <iostream>
#include <SFML/Graphics.hpp>

class Particle
{
public:
    float size{};
    sf::CircleShape shape;
    sf::Vector2f pos;


    Particle(float s) {
        size = s;
        shape = sf::CircleShape(size);
        shape.setFillColor(sf::Color::White);

    }
    void begin() {
        
        pos = sf::Vector2f(100, 100);

    }

    void tick(sf::RenderWindow& window) {
        
        pos.x += 10;
        shape.setPosition(pos);
        window.draw(shape);
        std::cout << pos.x;
    }

};

void tick(sf::RenderWindow& window, Particle particle) {
    window.clear();

    particle.render(window);

    window.display();
}



int main()
{
    sf::ContextSettings settings;
    settings.antialiasingLevel = 8;

    sf::RenderWindow window(sf::VideoMode(1500, 900), "MiniPhySim", sf::Style::Default, settings);

    sf::Clock clock;

    Particle particle(20);


    while (window.isOpen())
    {

        sf::Event event;
        while (window.pollEvent(event))
        {
            if (event.type == sf::Event::Closed)
                window.close();
        }


        tick(window , particle);

        sf::sleep(sf::seconds(0.5));


    }

    return 0;
}

What I thought happened is that the position value I’m incrementing is not the position of the instance object but I do not know how to access it. It works fine when I update the value from the the main function but I don’t want to because It’s obviously not a good idea.

>Solution :

Your problem is here:

void tick(sf::RenderWindow& window, Particle particle) {

You’re passing the Particle object by-value, which means that the particle inside the tick() method-call is a copy of the original Particle object from main(), and any modifications made to the copy get discarded when tick() returns; they don’t affect the original object in main() at all.

You can get the behavior you want by passing particle by-reference instead:

void tick(sf::RenderWindow& window, Particle & particle) {