- (void)viewDidLoad {
    [super viewDidLoad];
    CGRect rect = CGRectMake(0,0,340,480);
    UIView *ui = [[UIView alloc] initWithFrame:rect];
    [self.view addSubview:ui];
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextAddArc(context, 50, 50, 20, 0, 30, 0);
}

//set the fill or stroke color
CGContextSetRGBFillColor(context, 0.5, 0.5, 0.5 1.0);
CGContextSetRGBStrokeColor(context, 0.5, 0.5, 0.5, 1.0);

//fill or draw the path
CGContextDrawPath(context, kCGPathStroke);
CGContextDrawPath(context, kCGPathFill);