Defining constant for screen width

I ha开发者_如何学运维ve a constant defined with screen width to 320. This is being used at multiple places in my code. I have to change this to take value from current device and I do not want to touch all these places. So, I want to define a constant for this with value:

[[UIScreen mainScreen] bounds].size.width

#define kScreenWidth [[UIScreen mainScreen] bounds].size.width

But it is giving me lot of compilation errors. Any clue?

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[[UIScreen mainScreen] applicationFrame].size.width