Drawing Hollow circle in iPhone

Working further on what Ole Begemann referred in his answer and some modification, I was able to achieve the requirement.

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColorWithColor(context, [UIColor colorWithPatternImage:[UIImage imageNamed:@"background_grey_pattern.png"]].CGColor);
CGMutablePathRef path = CGPathCreateMutable();
CGContextSetLineWidth(context, 40);
CGPathAddArc(path, NULL, aRect.size.width/2, aRect.size.height/2, 45, 0*3.142/180, angle*3.142/180, 0);
CGContextAddPath(context, path);
CGContextStrokePath(context);
CGPathRelease(path);

So instead of 2 arcs I used only one and stroked it with higher width.

This is tangential but kind of relevant. Here's my Swift drawing code for a donut (or hollow circle).

class func drawDonut(donutColor: UIColor, rect: CGRect, innerDonutProportion: CGFloat) {

    //// Variable Declarations
    let innerDonutSide: CGFloat = rect.size.width * innerDonutProportion
    let innerDonutOffset: CGFloat = 0.5 * (rect.size.width - innerDonutSide)
    let innerDonutRect = CGRectMake(innerDonutOffset, innerDonutOffset, innerDonutSide, innerDonutSide)

    //// InnerCircle Drawing
    let innerCirclePath = UIBezierPath(ovalInRect: innerDonutRect)

    //// Outer Circle Drawing
    let outerCirclePath = UIBezierPath(ovalInRect: rect)

    // Clip out the innerCirclePath
    outerCirclePath.appendPath(innerCirclePath)
    outerCirclePath.addClip()
    outerCirclePath.usesEvenOddFillRule = true;

    // and Fill the outerCircle
    donutColor.setFill()
    outerCirclePath.fill()
}

Have a look at Filling a Path in the Core Graphics documentation. Basically, what you do is add two arcs to your path (the outer and the inner one) and then use Core Graphics fill rules to your advantage. The code would look something like this:

CGMutablePathRef path = CGPathCreateMutable();

// Add the outer arc to the path (as if you wanted to fill the entire circle)
CGPathMoveToPoint(path, ...);
CGPathAddArc(path, ...);
CGPathCloseSubpath(path);

// Add the inner arc to the path (later used to substract the inner area)
CGPathMoveToPoint(path, ...);
CGPathAddArc(path, ...);
CGPathCloseSubpath(path);

// Add the path to the context
CGContextAddPath(context, path);

// Fill the path using the even-odd fill rule
CGContextEOFillPath(context);

CGPathRelease(path);