UITextField percent

ViewController.m

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    if (textField == self.percentTextField) {
        NSString *text = textField.text;
        if ([string length] == 0 && range.length > 0) { //if delete last symbol
            if (text.length > 0) {
                text = [text substringToIndex:[text length] - 2];
                textField.text = text.length > 0 ? [NSString stringWithFormat:@"%@%%",text] : @"";
            }
        } else {
            text = [text stringByReplacingCharactersInRange:range withString:string];
            text = [text stringByReplacingOccurrencesOfString:@"%" withString:@""];
            textField.text = [NSString stringWithFormat:@"%@%%",text];
        }
        return NO;
    }
}