ios - Restricting the number of characters entered in UiTextfield by user

Question

I am trying to restrict the number of characters entered in UITextfied,I want the user to enter the numbers in range 40.[0 to 9] to 250.[0 to 9] and the user can only one digit after the decimal point and also he cant enter multiple decimal points. I hope I have made my point clear, so far I have tried some code which is below

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string 
{
    NSCharacterSet *nonNumberSet = [[NSCharacterSet characterSetWithCharactersInString:@"0123456789."] invertedSet];

    // allow backspace
    if (range.length > 0 && [string length] == 0) {
        return YES;
    }
    // do not allow . at the beggining
    if (range.location == 0 && [string isEqualToString:@"."]) {
        return NO;
    }   
    // set the text field value manually
    NSString *newValue = [[textField text] stringByReplacingCharactersInRange:range withString:string];
    newValue = [[newValue componentsSeparatedByCharactersInSet:nonNumberSet] componentsJoinedByString:@""];
    textField.text = newValue;
    // return NO because we're manually setting the value
    return NO;
}

So friends please help me further.

Regards Ranjit