ios 输入框输入6位数字

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{

    if (textField.tag == 11) {
        //新密码
                if(range.location <= 5){
                    
                            if ([string length]>0)
                            {
                                unichar single=[string characterAtIndex:0];//当前输入的字符
                                if ((single >='0' && single<='9'))//数据格式正确
                                { 
                                    return YES; 
                                }else{ 
                                    return NO; 
                                } 
                            }else{ 
                                return YES; 
                            }
                    
                }else{
                    
                    return NO;
                }
    }else{
        //确认新密码
        if(range.location <= 5){
            
            if ([string length]>0)
            {
                unichar single=[string characterAtIndex:0];//当前输入的字符
                if ((single >='0' && single<='9'))//数据格式正确
                {
                    return YES;
                }else{
                    return NO;
                }
            }else{
                return YES;
            }
            
        }else{
            
            return NO;
        }
    }
}