iOS-Requirement

#if __IPHONE_OS_VERSION_MIN_REQUIRED <= __IPHONE_6_1
  //code here
#endif

iphone-version-ref

#define __IPHONE_2_0     20000
#define __IPHONE_2_1     20100
#define __IPHONE_2_2     20200
#define __IPHONE_3_0     30000
#define __IPHONE_3_1     30100
#define __IPHONE_3_2     30200
#define __IPHONE_4_0     40000
#define __IPHONE_4_1     40100
#define __IPHONE_4_2     40200
#define __IPHONE_4_3     40300
#define __IPHONE_5_0     50000
#define __IPHONE_5_1     50100
#define __IPHONE_6_0     60000
#define __IPHONE_6_1     60100
#define __IPHONE_7_0     70000
#define __IPHONE_NA      99999  /* not available */