Mine

int isInt(string theString) throw ()
{
	//destroy whitespace at beginning and end of string.
	theString = destroyWhitespace(theString);
	
	const string integerList("0123456789");
	int start = 0;
	bool negative = false;
	const int maxListIndex = integerList.length()-1;
	const int maxStringIndex = theString.length()-1;

	//check for minus or plus at beginning of integer.
	try
	{
		if(theString.at(0) == '-') 
		{
			start = 1;
			negative = true;
		}
		else if(theString.at(0) == '+') 
		{
			start = 1;
		}
	}
	catch(...)
	{
		throw;
	}

	//Loops through valid digits to check.
	int index = start;
	while( index <= maxStringIndex ) 
	{
		bool match = false;
		
		try
		{
			for( int j = 0; (match == false) && (j <= maxListIndex); j++ ) 
			{
				if(theString.at(index) == integerList.at(j)) 
				{
					match = true;
				}
			}
			
			if (match == false) 
			{
				throw string("String is not a valid integer.");
			}
		}
		catch(...)
		{
			throw;
		}

		index++;
	}
	
	//Construct number.
	int number;
	int factor;
	try
	{
		number = theString.at(maxStringIndex) - '0';
		factor = 1;
		for(index = maxStringIndex-1; index >= start; index--)
		{
			factor *= 10;
			number += factor * (theString.at(index)-'0');
		}
	}
	catch(...)
	{
		throw;
	}
	//Change negative if needed.
	if(negative == true)
		number *= -1;
	return number;
}