pinch zooming

Hello. Please tell me how can a cocos2d-x zooming to implement?
@
void HelloWorld::ccTouchesMoved(cocos2d::CCSet* touches, cocos2d::CCEvent* event)
{
if( touches~~>count ==2)
{
CCTouch *touch = touches~~>anyObject();
}
@
How now do to zoom in and zoom out the screen?
Please,help me)