2. circle c = new circle(100,75,5,5,30); 
3. 
   
4. void setup() {size(400, 400);
5.               frameRate(30);
6.               smooth();
7.               }
8. 
   
9. void draw(){ background(204);
10.              c.mover();
11.              c.display();
12.              fill(35,40,232);
13.              rect(115,90,195,220); } 
14.  
15. class circle { 
16.   float x,xs,y,ys,r,x1,y1;
17.     
18.     circle (float xpos, float ypos,float xspeed,float yspeed,float radi) {  
19.     x=xpos;
20.     y=ypos;
21.     xs=xspeed;
22.     ys=yspeed;
23.     r=radi;
24.     
25. } 
26.   
27.   
28.   
29.    void mover() {if(key == 'a'){
30.      
31.      x+=xs;
32.    if(x == 325)
33.     {xs=0; ys=5; y+=ys;}
34.    if(y == 325)
35.     {ys=0; xs=-5;}
36.    if(x == 100)
37.     {xs = 0; ys = -5; y+=ys;}
38.    if(y == 75)
39.     {ys=0; xs=5;}}}
40.   
41.   void display(){ 
42.      
43.     fill(250,0,205);  
44.     ellipse(x,y,r,r); 
45.   } 
46. }

Here is my code and there is a circle moving around a rectangle. I want to initiate it with using 'a' key and stop it with using 'b' key.I can start it with pressing 'a'. However if I press any other keys(like 'd' or 'i') circle stops moving around the rectangle. I just want to stop my circle with using 'b' key. Can someone help me? Thanks.