Programming Praxis

4 Responses to “ATM Machine”

1. matthew said

   February 26, 2019 at 11:49 PM

   Your suggested solution has a large chunk missing (comparing with the ideone version, looks like a section in angle brackets has disappeared).
2. programmingpraxis said

   February 27, 2019 at 2:13 AM

   @matthew: Thanks. I think it’s fixed now. On the other hand, last night when I edited the exercise it looked right, too. WordPress has been playing with their editor lately, improving it. Things may change tomorrow.
3. Daniel said

   March 4, 2019 at 4:48 AM

   Here’s a solution in Python.

   database = {
       'user1': ['password1', 20],
       'user2': ['password2', 100],
       'user3': ['password3', 0],
   }
   
   while True:
       user = input('user> ')
       password = input('password> ')
       entry = database.get(user)
       if entry is None or entry[0] != password:
           print('login error')
           continue
       menu = (
           '[q] quit\n'
           '[d] deposit\n'
           '[w] withdraw'
       )
       while True:
           balance = entry[1]
           print('balance: {}'.format(balance))
           print(menu)
           option = input('choice> ')
           if option == 'q':
               break
           elif option == 'd':
               amount = int(input('amount> '))
               entry[1] += amount
           elif option == 'w':
               amount = int(input('amount> '))
               if amount > balance:
                   print('insufficient funds')
               else:
                   entry[1] -= amount
   

   Example:

   user> user4
   password> password4
   login error
   user> user2
   password> password2
   balance: 100
   [q] quit
   [d] deposit
   [w] withdraw
   choice> d
   amount> 5
   balance: 105
   [q] quit
   [d] deposit
   [w] withdraw
   choice> w
   amount> 200
   insufficient funds
   balance: 105
   [q] quit
   [d] deposit
   [w] withdraw
   choice> q
   user> 
   
4. Tim said

   March 22, 2019 at 1:49 PM

   Scheme version for completeness:

   (import (chicken io) simple-md5 srfi-69)
   
   (define account-db (make-hash-table))
   
   (define (prompt-for-line prompt)
     (print* prompt)
     (read-line))
   
   (define (get-value prompt)
     (let ((v (string->number (prompt-for-line prompt))))
       (if (and v (>= v 0))
           v
           (begin
             (print "Invalid amount.")
             (get-value prompt)))))
   
   (define (make-account-dispatcher value)
     (define (dispatch)
       (print "\nYou currently have " value " CHF.\n\n"
              "Options:\n"
              "- [D]eposit funds\n"
              "- [W]ithdraw funds\n"
              "- e[X]it")
       (case (string->symbol (prompt-for-line "> "))
         ((D d) (let ((v (get-value "Amount to deposit: ")))
                  (set! value (+ value v))
                  (dispatch)))
         ((W w) (let ((v (get-value "Amount to withdraw: ")))
                  (if (> v value)
                      (print "Insufficient funds!")
                      (set! value (- value v)))
                  (dispatch)))
         ((X x) (print "Don't forget your card."))
         (else (print "Invalid option.")
               (dispatch))))
     dispatch)
   
   (define (make-login username password)
     (cons username
           (string->md5sum (string-append username password))))
   
   (define (get-login)
     (make-login
      (prompt-for-line "Username --> ")
      (prompt-for-line "Password --> ")))
   
   (define (add-account login funds)
     (hash-table-set! account-db login (make-account-dispatcher funds)))
   
   (define (open-account)
     (print "Assign name and password for new account:")
     (add-account (get-login) 0)
     (print "Account created.  You may now log in."))
   
   (define (atm)
     (print "\nWelcome to E-Corp ATM\n"
            "=====================\n")
     (let ((login (get-login)))
       (if (hash-table-exists? account-db login)
           ((hash-table-ref account-db login))
           (print "** Error: Invalid account."))
       (atm)))
   
   (add-account (make-login "user1" "pass1") 10)
   (add-account (make-login "user2" "pass2") 20)
   (add-account (make-login "user3" "pass3") 30)
   
   (atm)
   

   Example output:

   $ csi atm.scm
   
   Welcome to E-Corp ATM
   =====================
   
   Username --> user1
   Password --> pass1
   
   You currently have 10 CHF.
   
   Options:
   - [D]eposit funds
   - [W]ithdraw funds
   - e[X]it
   > d
   Amount to deposit: 123
   
   You currently have 133 CHF.
   
   Options:
   - [D]eposit funds
   - [W]ithdraw funds
   - e[X]it
   > w
   Amount to withdraw: 12
   
   You currently have 121 CHF.
   
   Options:
   - [D]eposit funds
   - [W]ithdraw funds
   - e[X]it
   > x
   Don't forget your card.