Arc4random error: "Invalid operands to binary expression ('float' and 'float')"

Arc4random error: "Invalid operands to binary expression ('float' and
'float')"

I want to create a button at random position in certain view. I searched
and read some SO topics however I couldn't find the solution for my
problem.
Here is my code:
UIButton *button1 = [UIButton buttonWithType:UIButtonTypeCustom];
CGRect buttonRect = button1.frame;
buttonRect.size = CGSizeMake(100, 100);
button1.frame = buttonRect;
[self.arr addObject:button1];
int r = ([button1 frame].size.width)/2;
int x = r + (arc4random() % (self.view.frame.size.width -
button1.frame.size.width));
int y = r + (arc4random() % (self.view.frame.size.height -
button1.frame.size.height));
//ERROR:Invalid operands to binary expression ('float' and 'float')
[button1 setCenter:CGPointMake(x, y)];