4.1 Fundamentals of programming

Question 1

What is a recursive subroutine?

Answer 1

One that calls itself (or is defined in terms of itself)

Question 2

3 advantages of recursion

Answer 2

1. Can lead to very elegant, short code
2. People think recursively (sometimes)
3. It is sometimes the only way to solve a problem

Question 3

2 disadvantages of recursion

Answer 3

1. Can be slower than iterative solutions
2. Can use more memory than iterative solutions

Question 4

What is a global variable?

Answer 4

A variable that can be accessed from any part of a program

Question 5

What error will occur if a recursive subroutine never meets its base case?

Answer 5

Stack overflow

Question 6

3 items stored in a stack frame

Answer 6

• Return address
• Parameters
• Local variables

Question 7

What is meant by a ‘base case’?

Answer 7

The terminating situation in a recursive procedure that does not use recursion to produce a result

Question 8

What is meant by iteration?

Answer 8

Repeating an instruction

Question 9

What is a subroutine? (2*)

Answer 9

• A named block of code containing a set of instructions designed to performed a frequently used operation
• It can be called from other parts of the program using its identifier

Question 10

What type of iteration is it when the number of repetitions is not required to be known before the loop starts?

Answer 10

Indefinite iteration

Question 11

2 advantages of using constants over hard-coded values

Answer 11

1. Constants can be given identifier names, making code easier for a human to understand
2. When updating a value, constants only need updating at one position in code

Question 12

What is the advantage of favouring composition over inheritance?

Answer 12

It makes it easier to test each class using unit testing

Question 13

Similarity between composition and aggregation

Answer 13

Both “has a” relationships (ownership)

Question 14

Difference between composition and aggregation

Answer 14

• In composition, if the containing object is destroyed so are the objects it contains
• This is not the case with aggregation

(composition = strong ownership, aggregation = weak ownership)

Question 15

5 advantages of using subroutines

Answer 15

• Code re-use
• Allows for modularisation of the program
• It makes it easier to identify bugs
• It makes it easier to test individual tasks NE easier to test
• It makes it easier for other programmers to interpret and understand your code

Question 16

What is a syntax error? (2*)

Answer 16

• Occurs before program is run
• Code can’t be compiled

Question 17

What is a runtime error? (2*)

Answer 17

• Occurs while the program is running
• Causes the program to crash

Question 18

What is a logic error? (3*)

Answer 18

• Occurs while the program is running
• Made by the programmer
• Doesn’t cause the program to crash

Question 19

Suggest a way to fix a logic error?

Answer 19

By tracking variable values or dry running using a trace table

Question 20

What is an object reference variable? (2*)

Answer 20

• A fixed length memory address that points to a memory location (in the heap)
• It is used to refer to an object

Question 21

What is the purpose of a class?

Answer 21

To define the method and property fields that capture the common behaviours and characteristics of objects

Question 22

How is composition represented in UML?

Answer 22

Black diamond

Question 23

How is aggregation represented in UML?

Answer 23

White diamond

Question 24

What is encapsulation? (2*)

Answer 24

• The process of combining properties and methods together into an object
• and being able to restrict access to an object’s state / behaviour

Question 25

What is a constructor?

Answer 25

A method that is called when an object is first created

Question 26

What is the purpose of inheritance?

Answer 26

To create a hierarchy of specialisation for classes

Question 27

What is (subtype) polymorphism? What is its purpose? (3*)

Answer 27

• When a method in a parent class also exists in a derived class
• The method has the same name and parameter list, but a different implementation
• It allows objects up and down the inheritance hierarchy chain to respond differently to the use of a common interface

Question 28

2 advantages of “programming to interfaces, not implementation”

Answer 28

• Allows you to test each part of your program separately
• Allows you to modify your code easily in the future

Question 29

2 advantages of local variables over global variables

Answer 29

• You can give local variables the same name in different subroutines because they are only recognised by the subroutine they are declared in
• Local variables are deleted as soon as the subroutine is over and release the memory space which it occupies

Question 30

What is a constant?

Answer 30

A data item that, once declared, retains the same value for the entire duration of the program run

Question 31

2 advantages of using constants over local variables

Answer 31

• Makes your code more readable, by clearly indicating that a value should not be changed throughout the program
• Enhances code safety by preventing accidental modifications to values that shouldn’t change

Question 32

What does the access modifier protected mean? Give its UML symbol

Answer 32

• It can be accessed by any subclasses
• and from within the class itself
• #

Question 33

What does the access modifier public mean? Give its UML symbol

Answer 33

• It can be accessed by any class
• +

Question 34

What does the access modifier private mean? Give its UML symbol

Answer 34

• It can only be accessed from within the class
• -

Question 35

What is the purpose of a hierarchy chart?

Answer 35

• To represent the structure of the program
• By showing which subroutine is called from which subroutine

Question 36

Constructing a hierarchy chart aids with which type of abstraction?

Answer 36

Decomposition
(possibly others)

Question 37

What is meant by a structured programming approach?

Answer 37

• When decomposition of a problem occurs by using block structures (subroutines)
• Structured programming makes use of control structures - sequence / selection / iteration

Question 38

What are user-defined data types?

Answer 38

Data types that are derived from existing built-in types in order to create a customised data structure

Question 39

3 advantages of OOP

Answer 39

• Classes are highly modular, meaning they are easy to maintain
• Promotes code reuse
• Encapsulation provides a high level of protection for data

Question 40

2 drawbacks of OOP

Answer 40

• Can lead to very large and complex systems
• Objects can take up a relatively large amount of memory, which is an issue if there are hardware restrictions

Question 41

What is meant by favouring composition over inheritance?

Answer 41

Using objects composed of other objects rather than a tightly coupled inheritance system as it allows for more flexibility

Question 42

Describe the “encapsulate what varies” design principle

Answer 42

When designing a program in the OOP, any requirements ​which are likely to change in the future ​should be ​encapsulated in a class ​so that any changes can be​ easily made when required​.

Question 43

Name 3 OOP design principles

Answer 43

• Encapsulate what varies
• Favour composition over inheritance
• Program to interfaces, not implementation