hi, how do i make ellipse in this code to start shrinking-expanding-shrinking-expanding
not like right now expanding-shrinking...etc.

float x=0;
void setup(){
size(200,200);
smooth();
}

void draw(){
background(127);
x=x+1;
if (x>width){
x=-x;
}
ellipse(width/2,height/2,x,x);
}

//my attempt (fails)

float x=200;
void setup(){
size(200,200);
smooth();
}

void draw(){
background(127);
x=x-1;
if (x<0){
x=+x;
}
if (x>width){
x=x+1;
}
ellipse(width/2,height/2,x,x);
}