購物車程序

需求:

1. 啓動程序後，讓用戶輸入工資，而後打印商品列表
2. 容許用戶根據商品編號購買商品
3. 用戶選擇商品後，檢測餘額是否夠，夠就直接扣款，不夠就提醒 
4. 可隨時退出，退出時，打印已購買商品和餘額

salary = int(input("Input your salary: "))
goods = ['iphone', 'book', 'desk', 'cup']
price = [5800, 20, 55, 35]
for i in range(4):
	print(i+1, '--', goods[i], '--', price[i])
cost = 0
cart = []
while True:
	buy = input("Which would you want? ")
	if buy.isdigit():
		buyid = int(buy)
		if buyid >= 1 and buyid <= 4:
			cost += price[buyid-1]
			if cost > salary:
				print("No stufficient funds. Try again.")
				cost -= price[buyid-1]
				continue
			cart.append(goods[buyid-1])
			print("  Your cost is ", cost, ", Your balance is ", salary-cost)
		else:
			print("Input between 1 and 4.")
			continue
	elif buy == 'q':
		for i in cart:
			print(i, )
		print("  Your cost is ", cost, ", Your balance is ", salary-cost)
		break
	else:
		print("Input between 1 and 4, or q(quit).")
		continue