user input: **HELLO**!!

what's suppose to happen:
firstWord = HELLO
inspectThis = **!!

Code:
string extractWord (string& inspectThis)
{
	string firstWord;
	int i = 0;

	while (inspectThis[i] != '\n')
	{
		if (isalpha(inspectThis[i]))
		{
			firstWord += inspectThis[i];
			inspectThis[i] = NULL;
		}
		inspectThis[i] = NULL;
		i++;
	}
	return firstWord;
}
this is what i have so far and right now i'm stuck