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This is very well answered in StackOverflow.

// Version is the readable dot notation eg `1.2.3` or `5.0`
NSString *version = [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleShortVersionString"];

// Build can be any string eg `789` or `8A400`
NSString *build = [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleVersion"];