Boolean functions with strings

[geo28t]

SO i am in a bit of a predicament. For an assignement, I am asked to create a boolean function that includes a string (Specifically, one called bool (isValidEbayListingString(string auctionstring)). I know that a boolean function is supposed to return true or false statements. One of the ones I have written tells the code to produce a false statement if an empty string is input. However, how would I make it so that when the user enters a letter next to a number, it turns out true? Thanks?

  bool isValidEbayListingString(string auctionstring)
{
	bool result = true;

	int num;



	if (auctionstring.length() == 0)
	{
		result = false;
	}
	return result;
}