final private void createAndAddVariable(String variableRepresentation) throws InvalidInputException
	{
		//ignore empty variable names 
		if (variableRepresentation.trim().equals(""))
		{
			return;
		}
		//find the variable and then add it to the tokenized expression
		for (int variableIndex = 0; variableIndex < this.m_variables.size(); variableIndex++)
		{
			Variable aVariable = this.m_variables.get(variableIndex);
			if (variableRepresentation.equals(aVariable.getRepresentation()))
			{
				this.m_tokenizedExpression.addElement(new Variable(variableRepresentation, aVariable.getValue()));
				return;
			}
		}
		throw new InvalidInputException(Text.CALCULATIONS.getInvalidNumberMessage(variableRepresentation));
	}