系统版本的判断
<pre><code>
/*

• System Versioning Preprocessor Macros
  */

define SYSTEM_VERSION_EQUAL_TO(v) ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedSame)

define SYSTEM_VERSION_GREATER_THAN(v) ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedDescending)

define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v) ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)

define SYSTEM_VERSION_LESS_THAN(v) ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedAscending)

define SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(v) ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedDescending)

/*

• Usage
  */

if (SYSTEM_VERSION_LESS_THAN(@"4.0")) {
...
}

if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"3.1.1")) {
...
}

或者

define IS_IPHONE5 (([[UIScreen mainScreen] bounds].size.height-568)?NO:YES)

define IS_OS_5_OR_LATER ([[[UIDevice currentDevice] systemVersion] floatValue] >= 5.0)

define IS_OS_6_OR_LATER ([[[UIDevice currentDevice] systemVersion] floatValue] >= 6.0)

define IS_OS_7_OR_LATER ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0)

define IS_OS_8_OR_LATER ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0)

</code></pre>

APP版本的判断
<pre><code>

• (NSString *) appVersion
  {
  return [[NSBundle mainBundle] objectForInfoDictionaryKey: @"CFBundleShortVersionString"];
  }
  </code></pre>

build版本判断
<pre><code>

• (NSString *) build
  {
  return [[NSBundle mainBundle] objectForInfoDictionaryKey: (NSString *)kCFBundleVersionKey];
  }
  </code></pre>

参考链接：
How to check iOS version?

Best Way to check for iOS 7 or earlier?