int ballY
forgot something ?

im geting an erro again……… cannot find anything named c??

your code is pretty buggy !
What are trying to do ?
I suggest you to read about classes and how to construct them.

The display of ball is handled by the Ball class. No need to draw it with ellipse outside the class.
You just need to call display function from Ball class to display the ellipse.

1. Ball b; // instant of the object
2. void setup()
3. {
4.   size(400, 400);
5.   background(255);
6. } 
7. void draw()
8. {
9.   smooth();
10.   line(0, height/2, width, height/2);
11.   line(width/2, 0, width/2, height);
12.   //b.display();
13. } 
14. void mousePressed()
15. {
16.   b= new Ball();
17.   b.display();
18. }
19. class Ball
20. {
21.   //data memebers declarations
22.   int radius;
23.   color c;
24.   //position of the ball
25.   int ballX; //position of the ball on x-axis
26.   int ballY; //position of the ball on y-axis
27.   //constructor(data member inialisations)
28.   Ball()
29.   {
30.     radius = 50;
31.     c = color(random(0, 256), random(0, 256), random(0, 256));
32.     ballX = (int) random(radius, width-radius);
33.     ballY = (int) random(radius, height-radius);
34.   }
35.   //method
36.   void display()
37.   {
38.     fill(c);
39.     ellipse(ballX, ballY, radius, radius);
40.   }
41. }

thx