Check iOS version

if (floor(NSFoundationVersionNumber) > NSFoundationVersionNumber_iOS_6_1) {
    // here you go with iOS 7
}

ModalViewController transparent background

[viewController setModalPresentationStyle:UIModalPresentationOverCurrentContext];

Check if the entered text uses only English letters

NSCharacterSet* tSet = [NSCharacterSet characterSetWithCharactersInString:
               @"abcdefghijklmnopqrstuvwxyz1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ"];
    NSCharacterSet* invSet = [tSet invertedSet];
    NSString* legalS = @"abcdA1";
    NSString* illegalS = @"asvéq1";

    if ([legalS rangeOfCharacterFromSet:invSet].location != NSNotFound)
        NSLog(legalS); // not printed

    if ([illegalS rangeOfCharacterFromSet:invSet].location != NSNotFound)
        NSLog(illegalS); // printed