Find out if the device has iOS4 or iOS5 installed, and perform a version-specific action based on the results.

iOSVersionFinder

NSArray *versions = [[UIDevice currentDevice].systemVersion componentsSeparatedByString:@"."];
 
if ( 5 == [[versions objectAtIndex:0] intValue] ) { /// iOS5 is installed
    
    // Perform iOS-5 actions here

} else { /// iOS4 is installed
 
    // Perform iOS-4 actions here              
            
}