	takeExp();
	for(int i=0; i<exp.length(); i++)
	{
		c = exp.at(i);
		if((c >= "a" && c <= "z") || (c >= "A" && c <= "Z") || (c >= "0" && c <= "9"))
		{
			str = str + c;
		}
		else if(isEmpty() || peek() == "(")
			push(c);
		else if(c == "(")
			push(c);
		else if(c == ")")
		{
			while(!isEmpty() && peek() != "(")