Chapter 5: Excercises

This page contains a set of excercises for the corresponding chapter.
Read the task description, copy the code template if present and solve it in your Eclipse.
If you are stuck, you can show the solution for this task. Be careful not to spoil the solution for yourself unnecessarily.

Contents

1. Swap Values with References
2. Course Management

Swap Values with References

Your task is to:

1. Declare two variables as integer references in the main procedure, assign two different values to these variables.
   Afterwards print the values of the variables.
2. Implement a procedure swap which accepts two integer reference parameters.
   Swap the values of these parameters inside the operation.
3. Invoke the swap procedure from the main procudre and pass the previously declare variables as parameters.
   Print the values of the variables again, they should now be swapped.

The output of the program could look like this:

x = 42 y = 5 x = 5 y = 42

Show solution

program swapVars import IO operation swap(parameter a : reference<integer>, parameter b : reference<integer>) variable c : integer c := b@ b@ := a@ a@ := c endoperation main variable x : reference<integer> variable y : reference<integer> x := reference 42 y := reference 5 IO.writeString("x = ") IO.writeInteger(x@) IO.writeLine() IO.writeString("y = ") IO.writeInteger(y@) IO.writeLine() swap(x, y) IO.writeString("x = ") IO.writeInteger(x@) IO.writeLine() IO.writeString("y = ") IO.writeInteger(y@) IO.writeLine() endmain

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Course Management

Type Util

Declare a compostion called Util.
This composition should have a hidden integer attribute counter.
Futhermore, it should have a visible operation generateNumber() which does not accept any parameters and returns an integer.
Each time the operation is called, the value of counter should be incremented by 1 and then returned.

Test your implementation of Util, it should look like this:



Types Person and Docent

Declare an abstract compostion called Person.
A person has a hidden string attribute name, which should be still visible in its subtypes.
Implement an operation getName() which returns the name of the person.
This way we can not change the name of a person after its instantiation but have still reading access to it.

Now create a non-abstract type Docent as a subtype of Person

Test your implementation of Person and Docent, it should look like this:



Type Student

Declare a non-abstract compostion called Student which is also a subtype of Person.
In addition to the inherited features, each student has a immatriculationNumber,
which is a hidden integer attribute, but we should still have reading access to it similar to the attribute name.
Use the Util operation generateNumber() to generate immatriculation numbers.

Test your implementation of Student, it should look like this:



Type Course

Declare a non-abstract compostion called Course, all attributes should be hidden.

Each course has following features:

• A name.
• A maximum number of enrolled students.
• A reference to a docent.
• A list of enrolled students, which should also be referenced (e.g. attribute students : list<reference<Student>>).
• It should be possible to get all the information about a course by using a procedure printInfo().
• It should be possible to enrol a student using the procedure enrol(REFERENCE TO A STUDENT).
  Be aware that each course has a maximum number of enrolled students.
  If that number is reached, the enrollment process should fail with a corresponding message on the console.

The test program:

main variable util : Util variable d : reference<Docent> d := reference Docent{name = "Nikita"} variable k : reference<Course> k := reference Course{name = "Programming course", students = [], docent = d, maxNumberOfStudents = 3} variable s1 : reference<Student> s1 := reference Student{name = "Alice", immatriculationNumber = util.generateNumber()} variable s2 : reference<Student> s2 := reference Student{name = "Bob", immatriculationNumber = util.generateNumber()} variable s3 : reference<Student> s3 := reference Student{name = "Charlie", immatriculationNumber = util.generateNumber()} variable s4 : reference<Student> s4 := reference Student{name = "Dave", immatriculationNumber = util.generateNumber()} k@.enrol(s1) k@.enrol(s2) k@.enrol(s3) k@.enrol(s4) k@.printInfo() endmain

The output of the program could look like this:

Alice: enrollment successful. Bob: enrollment successful. Charlie: enrollment successful. Dave: enrollment is no longer possible. Course: Programming course Maximun number of students: 3 Docent: Nikita Enrolles are: Alice, immatriculation number: 1 Bob, immatriculation number: 2 Charlie, immatriculation number: 3

Show solution

program courseManagement import IO import Lists import Strings abstract type Person : composition protected attribute name : string operation getName() : string return name endoperation endtype type Student : composition extends Person private attribute immatriculationNumber : integer operation getImmatriculationNumber() : integer return immatriculationNumber endoperation endtype type Docent : composition extends Person endtype type Course : composition private attribute name : string private attribute students : list<reference<Student>> private attribute docent : reference<Docent> private attribute maxNumberOfStudents : integer operation printInfo() IO.writeString("Course:\n " & name & "\n") IO.writeString("Maximun number of students:\n " & Strings.integerToString(maxNumberOfStudents) & "\n") IO.writeString("Docent:\n " & docent@.getName() & "\n") IO.writeString("Enrolles are: \n") variable i : integer loop variable s : reference<Student> s := students[i] IO.writeString(" " & s@.getName() & ", immatriculation number: " ) IO.writeInteger(s@.getImmatriculationNumber()) IO.writeLine() i := i + 1 if i = Lists.lengthOf(students) then exit endif endloop endoperation operation enrol(parameter s : reference<Student>) if Lists.lengthOf(students) < maxNumberOfStudents then students := Lists.append(students, s) IO.writeString(s@.getName() & ": enrollment successful.\n") else IO.writeString(s@.getName() & ": enrollment is no longer possible.\n") endif endoperation endtype type Util : composition private attribute counter : integer operation generateNumber() : integer counter := counter + 1 return counter endoperation endtype main variable util : Util variable d : reference<Docent> d := reference Docent{name = "Nikita"} variable k : reference<Course> k := reference Course{name = "Programming course", students = [], docent = d, maxNumberOfStudents = 3} variable s1 : reference<Student> s1 := reference Student{name = "Alice", immatriculationNumber = util.generateNumber()} variable s2 : reference<Student> s2 := reference Student{name = "Bob", immatriculationNumber = util.generateNumber()} variable s3 : reference<Student> s3 := reference Student{name = "Charlie", immatriculationNumber = util.generateNumber()} variable s4 : reference<Student> s4 := reference Student{name = "Dave", immatriculationNumber = util.generateNumber()} k@.enrol(s1) k@.enrol(s2) k@.enrol(s3) k@.enrol(s4) k@.printInfo() endmain

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