CEng 242 Homework 3
Due: 7th April 2000

Define an abstract data type Wallet with the following features: It can contain cash (bills with values 1,5,10,25,100 only, and there can be at most 20 bills in a WALLET in total) and credit cards (card names are strings, and there can be at most 5 credit cards in a WALLET). Cash are tagged with CASH and credit cards are tagged with CARD. Each credit card also has a credit limit which is a positive integer less than 1000. All the cash can be ``assigned''from a WALLET to another WALLET.

Implement following functions and attributes:

• empty:Wallet
  Creates and returns an empty Wallet.
• addBill:Wallet->int*int->Wallet
  addBill w (bill,count) will add count bills of value bill to the wallet w and return the new wallet.
• addCard:Wallet->string*int->Wallet
  addCard w (name,limit) will add the new card with limit limit. If a credit card with the same name exists, new card will not be created but it is added to the credit of the existing card. Updated wallet will be returned.
• deleteBill:Wallet->int*int->Wallet
  deleteBill w (bill,count) will drop count of value bill in wallet and return the updated wallet.
• deleteCard:Wallet->string->Wallet
  deleteCard w s will delete the given credit card from wallet and return the updated wallet.
• cash:Wallet->int
  cash w will return the amount of the cash money in the wallet. Returns 0 if w is an invalid Wallet.
• credit:Wallet->int
  credit w will return the amount of credit available in all credit cards in the wallet. Returns 0 if w is an invalid Wallet.
• total:Wallet->int
  total w will return the amount of the cash money and total credit available in all credit cards. In other words, spendable amount in the wallet. Returns 0 if w is an invalid Wallet.
• pay:Wallet->int->Wallet
  pay w amount will pay the amount from the wallet using the following order:
  • If there are some bills in the wallet, try to pay partially or whole payment from bills.
  • If you cannot pay with the exact amount, but there are some bills left, try to give the minimal amount greater than the exact amount
  • If there is no enough bill in the wallet. Pay all bills, than pay the rest from credit cards.
  • Allways pay from the credit card with largest credit. If credit is not enough, combine several credit cards. Delete the credit card with 0 credit.
• display:Wallet->unit
  display w will display the wallet w on screen similar to the following example:

      1*4+5*2+10*0+25*1+3*100=339
      "UltraBank": 200
      "HiperBank": 175
      "HirsizBank": 950
      Credit: 1325 Total: 1664

Your abstract data type should produce the following invalid Wallet types:

• CreditOverFlow
  Result of addCard exceeds the credit per card limit 1000.
• CardOverFlow
  Result of addCard exceeds the number of cards 5.
• InvalidBill
  Argument of addBill or deleteBill is not a valid bill type.
• BillOverFlow
  Result of addBill exceeds the total bill number 20.
• CardnotFound
  Card name in deleteCard is not found.
• NotEnoughBill of int
  There is not enough number of bills in wallet for deleteBill request and int argument indicates the required number of bills to complete request.
• NotEnoughAmount of int
  There is not enough amount in the bills or credit cards to make the payment in pay request and int indicates the amount which could not be paid.
• InvalidWalletArg
  Wallet parameter of all functions other than display is an invalid Wallet.

display function should produce the following explanation for errors in the output. Type tags should be invisible to user.

CreditOverFlow "Credit limit for card is exceeded."
CardOverFlow "Too many cards."
InvalidBill "No such bill."
BillOverFlow "Too many bills."
CardnotFound "Card does not exist."
NotEnoughBill "Not enough bill of that type, %d is missing."
NotEnoughAmount "Not enough cash and/or credit, %d$ is missing."
InvalidWalletArg "Wallet argument is not a valid wallet."