private void saveExpression()
    {
        switch(Equation.getSelectedIndex()+1)
        {
            case 1:
                fx=getExpression();
                break;
            case 2:
                gx=getExpression();
                break;
            case 3:
                ax=getExpression();
                break;
            case 4:
                bx=getExpression();
                break;
            case 5:
                cx=getExpression();
                break;
            case 6:
                dx=getExpression();
                break;
            case 7:
                ex=getExpression();
                break;
        }
    }