func (c *Currency) SubtractInt(main int, frac int) {
	if main < 0 && frac > 0 {
		frac = -frac
	}
	c.UpdateWithFractional(c.FractionalTotal() - (main*int(c.FUShare) + frac))
}
SubtractInt subtracts main & fractional value provided from the currency
package currency
func (c *Currency) UpdateWithFractional(frac int) {
	fus := int(c.FUShare)
	c.Main = (frac / fus)
	c.Fractional = (frac % fus)
	if c.Main < 0 {
		c.Fractional = -c.Fractional
	}
}
func (c *Currency) Add(acur Currency) error {
	if c.Code != acur.Code {
		return ErrMismatchCurrency
	}
	c.UpdateWithFractional(c.FractionalTotal() + acur.FractionalTotal())
	return nil
}
func (c *Currency) AddInt(main int, frac int) {
	if main < 0 && frac > 0 {
		frac = -frac
	}
	c.UpdateWithFractional(c.FractionalTotal() + main*int(c.FUShare) + frac)
}