Chapter 4: objects
Questions

 
1.     What is the data structure of a basic type? What is the structure of a reference type? Draw an example of each.

2.     What happens when an object is created? State what happens when there is no creation routine for the class, and when there is a creation routine for the class. Why must a creation routine be a procedure?

3.     What code is needed in the client and in the supplier classes to create an object using a creation routine? If there is a creation routine in a class, can I create an object without calling that creation routine? Can a creation routine receive arguments? Can a class have several creation routines?

4.     Describe the mechanism used by Eiffel to find the code needed to execute a feature call from one client to another (object.feature). What happens when there is no explicit object mentioned? What is the value of Current?

5.     What is the difference between an operator and a function? What is an infix operator? What is a prefix operator? Give three examples of operators in Eiffel.

6.     Show the format of an infix operator definition. Write a definition for the infix operator #mod (modulus). What is the signature of this operator?

7. Define a class FAHRENHEIT that stores a temperature in degrees Fahrenheit. Define a class CELSIUS that stores a temperature in degrees Celsius (Centigrade). Write a function in FAHRENHEIT that returns a REAL number, the temperature in Centigrade. Write a function in CELSIUS that returns a REAL number, the temperature in Fahrenheit. Write a DRIVER root class to read in a single temperature, create the two objects, and display their values.

The basic form of the creation routine in the root class is

make is
                 -- drive the rest of the system
      local
                fahrenheit: FAHRENHEIT
                celsius: CELSIUS
        do
                io.putstring ("Enter the temperature in fahrenheit: ")
                io.readreal
                !!fahrenheit.make (io.lastreal)
                !!celsius.make (fahrenheit.to_celsius)
                fahrenheit.show
                celsius.show
        end -- make 8.     A farmer has 3 pigs. A pig has a name, weight, and age. Write a system that creates the three pigs, then shows their average weight. Write your system in the following stages:
a)     List the classes
b)     Draw a client chart
c)     For the class PIG, define the attributes and the signature and header for each routine
d)     For the root class FARMER, define the attributes, signatures, and headers
e)     Code the class PIG
f)      Code the class FARMER
g)     Run the system

9.     Look at the rock concert specification in Chapter 2, question 16. Change the solution from its procedural form to an OO form; that is, change it from a single block of code to a set of routines in a set of classes. Hint: you need to create three objects of the same class.

10.   Write equality functions for the classes POINT, LINE, and TRIANGLE. An equality function returns true if two objects are equal in some sense; here, two objects (of the same type) are equal if they are in the same location. An equality routine has the header

                is_equal (this: like Current): BOOLEAN is ...

The keyword like allows the type of an argument to be defined as "like this one".