Why is my button placed like that?

[quark]

@anna

button2X = width/2-(buttonSize/2);

The problem is that the width variable is not set until the size() method is executed in setup()

Change your code to

int buttonSize = 260;
int buttonY = 500; 
int button2X; 

and in setup

void setup(){
    size(480, 320); // use your own width and height
    button2X = width/2-(buttonSize/2); 
    // rest of your setup code
}