NSMutableArray *mutableTFs = [[NSMutableArray alloc] init];

for (UIView *view in [self.view subviews]) {
    if ([view isKindOfClass:[UITextField class]]) {
        [mutableTFs addObject:view];
    }
}

NSMutableArray *mutableTFs = [[NSMutableArray alloc] init];

for (UITextField *textField in [self.view subviews]) {
    [mutableTFs addObject:textField];
}

for (UIView *view in [self.view subviews]) {
    if ([view isKindOfClass:[UITextField class]]) {
        // you don't need to cast just to add to the array
        [mutableTFs addObject:view];
        // typecasting works as it does in C
        UITextField *textField = (UITextField *)view;
        // do something with textField
    }
}

for (UITextField *textField in [self.view subviews]) {
    if ([textField isKindOfClass:[UITextField class]]) {
        [mutableTFs addObject:textField];
    }
}

for (UIView *view in [self.view subviews]) {
    if ([view isKindOfClass:[UITextField class]]) {
        UITextField *textField = (UITextField *)view;
        // Do whatever you want with the text field.
    }
    if ([view isKindOfClass:[UITextView class]]) {
        UITextView *textView = (UITextView *)view;
        // Do whatever you want with the text view.
    }
}

// Make sure you're releasing this!
NSMutableArray *textFields = [[NSMutableArray alloc] init];

for (UITextField *textField in [self.view subviews]) {
    if ([textField isKindOfClass:[UITextField class]]) {
        [textFields addObject:textField];
    }
}