How do i save a variable in a loop to use it again later?

Question

I want to make a program which sets ellipses next to each other until one touches a border of my canvas and then proceeds in the other direction. Unfortunately it only works in one direction and stops when it hits the right border.Is there a way to save the sx variable at some point to use it again in the second if statement?

void setup() {
    size(700, 500);
    frameRate(20); // frame rate = 20 Hz
}

int sx=50;
int sy=50;
int dx=15;

void draw() {

    if(sx<width){
        ellipse(sx,sy,20,20); 
        sx=sx+dx;

        if(sx>width){
            sx=sx-dx;
        }
    }
}

Answer 1

sx is in global scope, so there is no need to "store" it, because the value is persistent.
What you want to do is quite simple. The key is dx rather than sx . If the the ellipse reaches the border of the window, the direction has to be changed. This can be achieved by inverting dx .

Invert dx ( dx *= -1 ) when sx is at the right border ( sx >= width ) or left border ( sx <= 0 ). eg:

void setup() {
    size(700, 500);
    frameRate(20); // frame rate = 20 Hz
}

int sx=50;
int sy=50;
int dx=15;

void draw() {

    background(196);
    ellipse(sx,sy,20,20); 
    sx=sx+dx;

    if (sx >= width || sx <= 0 ){
        dx *= -1;
    }
}