Excercises for the course "An Introduction to Procedural and Object-oriented Programming (Object Rexx)"

An overview of this course can usually be found at starting out of: http://wwwi.wu-wien.ac.at/Studium/.

Rony G. Flatscher, As of: 2004-10-26

Excercises (Loops)

A possible solution:

solutions/solution_01.rex

A possible solution:

solutions/solution_02.rex

Excercises (Functions)

A possible solution:

solutions/solution_03.rex

A possible solution:

solutions/solution_04.rex

A possible solution:

solutions/solution_05.rex

A possible solution:

solutions/solution_06.rex

Excercise 7: Euro Calculator

E.g. the invocation euro Ats 65 Dem should convert 65 Austrian Schillings into Deutsche Mark. If no target currency is given, then the amount should be converted to all Euro currencies, including the Euro itself.

Hint: starting with 1999-01-01 all Euro currencies are set to a fixed exchange rate with respect to one Euro (in 2001-01-01 the Greek Drachmen joined the Euro currency system) as follows:

A possible solution:

solutions/solution_07.rex

Excercises (Routines)

A possible solution:

solutions/solution_08.rex

A possible solution:

solutions/solution_09.rex

A possible solution:

solutions/solution_10.rex

A possible solution:

solutions/solution_11.rex

Excercise 12: Euro Calculator

In addition:

• Raise a user defined exception UNKNOWN_INPUT_CURRENCY or UNKNOWN_OUTPUT_CURRENCY, if the user enters an unknown Euro currency.

• If no input currency is given default to EUR.

A possible solution:

solutions/solution_12.rex

Excercises (ADT)

• attribute currency: stores the currency's name, e.g. ATS for the Austrian Schilling.

• attribute country: stores the country's name, e.g. Austria.

• attribute denotation: stores the name of the currency in the country's language, e.g. Schilling.

• attribute exchangeRate: stores the currency amount which is equivalent to 1 EUR (cf. table in excercise 7), e.g. 13.7603.

• function Currency2Euro: retrieves the currency amount as an argument and returns the equivalent Euro amount.

• function Euro2Currency: retrieves the Euro amount as an argument and returns the equivalent currency amount.

With the help of initialisation of new objects, the attributes denotation, exchangeRate, country and currency should get their values assigned to.

After creating such Euro objects one can use them to carry out the conversion calculations.

The following statements:

    /* arguments: "currency", "country", "denotation" and "exchangeRate" */
    o = .euro ~ NEW("ATS", "Austria", "Schilling", 13.7603)

    SAY o~denotation o~exchangeRate o~country o~currency
    SAY
    SAY "100" o~currency "are:" o~currency2euro(100) "EUR"
    SAY "100 EUR are:"          o~euro2currency(100) o~currency

    Schilling 13.7603 Austria ATS

    100 ATS are: 7.26728342 EUR
    100 EUR are: 1376.0300 ATS

A possible solution:

solutions/solution_13.rex

solutions/solution_13.cls

• The functions Currency2Euro and Euro2Currency are not needed anymore and therefore can be removed.

• The values of the following attributes must be set at initialisation time of EURO objects only: currency, country, denotation and exchangeRate.

  Hint for solving this particular demand: If a METHOD directive is processed by the interpreter, then in effect it will create two methods: one for setting a value in an attribute ("assignment"/"set" method) and one for getting the value stroed in an attribute ("access"/"get" method).

  Example for defining an attribute xyz with the help of a METHOD directive:

     ::METHOD xyz ATTRIBUTE 

  Given the above directive the interpreter will create the following two methods, before the program starts:

     ::METHOD XYZ  /* get method, returning the present attribute's value */
       EXPOSE XYZ  /* establish access to attribute         */
       RETURN XYZ  /* return value stored with attribute    */

     ::METHOD "XYZ=" /* set method, assigning a new value to the attribute */
       EXPOSE  XYZ   /* establish access to attribute       */
       USE ARG XYZ   /* retrieve argument and assign it to the attribute */

  In order to solve this task you need to make sure that the values for the attributes are set in the INIT method.
  Next, do not use method directives with the keyword ATTRIBUTE, rather create the needed "get" methods to retrieve the attribute's values yourself.

• Each EURO object shall receive an attribute for storing the euro_amount: if the amount is changed, then the euro_amount shall be re-calculated and vice versa (a change in the euro_amount automatically causes the amount to be re-calculated). For this purpose define the following two new attributes: amount and euro_amount.

  If creating a new EURO object an optional fifth argument should be allowed which - if given - sets the initial value of the amount attribute. If this argument is not given, then make sure that amount and euro_amount are set to 0.

  Hint for solving this particular demand: define the get and the set method yourself!

With the help of initialisation of new objects, the attributes denotation, exchangeRate, country, currency and, optionally, amoutn should get their values assigned to.

After creating such Euro objects one can use them to carry out the conversion calculations, by merely setting the value of the attribute amount or euro_amount and afterwards getting the value of the other attribute.

The following statements:

    /* arguments: "currency", "country", "denotation" and "exchangeRate" */
    o = .euro ~ NEW("ATS", "Austria", "Schilling", 13.7603)

    SAY o~denotation o~exchangeRate o~country o~amount o~currency  o~euro_amount "EUR"
    SAY
    o~amount = 100       -- set currency amount
    SAY o~amount o~currency "are:" o~euro_amount "EUR"
    o~euro_amount = 100  -- set euro amount
    SAY o~euro_amount   "EUR are:" o~amount o~currency

    Schilling 13.7603 Austria 0 ATS 0 EUR

    100 ATS are: 7.26728342 EUR
    100 EUR are: 1376.0300 ATS

A possible solution:

solutions/solution_14.rex

solutions/solution_14.cls

Excercises (Collection Classes)

A possible solution:

solutions/solution_14.rex

• List all type of fruits of the fruit bag, distinguish between the ordered and unordered types.

• List all type of fruits of the fruit bag, distinguish between the ordered and unordered types, giving the count of each.

  Make sure that you list the ordered fruits in exactly the following (alphabetic) order:

  • apple
  • banana
  • pear
  • plum

According to the content as given in excercise 16 the output now should look like as follows:

Received Fruits (ordered)
                 plum
                 pear
                apple
               banana

Received Fruits (not ordered)
               peanut
           strawberry
                melon
                mango
            pineapple

Received Fruits (ordered)
                apple:   9
               banana:   7
                 pear:   6
                 plum:   5

Received Fruits (not ordered)
               peanut:  20
           strawberry:   1
                melon:   3
                mango:   1
            pineapple:   4

Devise a program which solves this problem.

A possible solution:

solutions/solution_16.rex

Excercise(s) (Advanced)

   /* solution_17.rex */

   .test~~new("Anton") ~~new("Berta") ~~new("Caesar") -- create three instances

   SAY "Before synchroneous broadcast..."
   .test~broadcast( .message~new(.nil, "say_info"), .true )
   SAY "after synchroneous broadcast."
   SAY

   SAY "Before Asynchroneous broadcast..."
   .test~broadcast( .message~new(.nil, "say_info"))
   SAY "after asynchroneous broadcast."

   ::REQUIRES "solution_17.cls"

   /* --------------------------- Test-Class -------------------------------- */
   ::CLASS test            METACLASS Manager 

   /* --------------------------- Class Methods ----------------------------- */
   ::METHOD Init           CLASS 
     EXPOSE counter
     counter=0
     self~init:super

   ::METHOD count          CLASS 
     EXPOSE counter
     counter=counter+1
     RETURN counter

   /* --------------------------- Instance Methods -------------------------- */
   ::METHOD Init
     EXPOSE  name number
     USE ARG name
     number=self~class~count
     self~init:super

   ::METHOD name                 ATTRIBUTE

   ::METHOD say_info 
     EXPOSE number
     SAY " SAY_INFO - name:" self~name "created as #" number

   Before synchroneous broadcast...
   Manager.Broadcast: invoking messages synchroneously...
    SAY_INFO - name: Caesar created as # 3
    SAY_INFO - name: Berta created as # 2
    SAY_INFO - name: Anton created as # 1
   after synchroneous broadcast.

   Before Asynchroneous broadcast...
   Manager.Broadcast: invoking messages asynchroneously...
   after asynchroneous broadcast.

    SAY_INFO - name: Caesar created as # 3
    SAY_INFO - name: Berta created as # 2
    SAY_INFO - name: Anton created as # 1

A possible solution:

solutions/solution_14.rex

solutions/solution_14.cls

Hints for OODIALOG Rexx Programs