Programming:theory

Question 1

Describe the halting problem

Answer 1

Determining, given a program and input, whether or not the program will halt
{determining if a program will halt without running the program for a particular input}

Question 2

Why can’t the halting problem be simulated with a turning machine?

Answer 2

The halting problem is non-computable, a program cannot be written that determines whether a given algorithm will halt for a specified input.

Question 3

What are the components of a turing machine?

Answer 3

-infinite tape
-read/write head
-control unit
-finite set of states
-transition rules
-set of accepting/ halting states

Question 4

What is a UTM?

Answer 4

Universal turing machine

Question 5

What is a UTM?

Answer 5

-UTMs can simulate the behaviour of any other turing machine, and so can compute any computable sequence.
-Can act as an interpreter, taking data, programs or any other turing machine as an input

Question 6

Why are UTMs more powerful than any other computer?

Answer 6

Because it has an infinite amount of memory/tape

Question 7

What is an advantage of using constants?

Answer 7

-speed increases when run
-easier to read and maintain
-values only need to be assigned

Question 8

Define a global variable

Answer 8

A variable that can be referenced/accessed from any point in the program.

Question 9

Define a local variable

Answer 9

Can only be referenced/accessed within the subroutine it is defined in

Question 10

What is an advantage of local variable usage?

Answer 10

-avoids redundant memory usage, as variable value is no longer stored once subroutine is finished executing

Question 11

define the term record

Answer 11

A collection of fields, each of which could have a
different data type. You can think of a record as a row
from a table

Question 12

define a pointer or reference

Answer 12

A way of storing memory addresses

Question 13

what are the key features of an array?

Answer 13

-finite
-indexed
-same data type

Question 14

what are user defined data types?

Answer 14

derived from existing data types in order to create a customised data structure

Question 15

why are meaningful identifier names important?

Answer 15

-easier for others to understand
-means maintenance is easier
-collaborative programming is easier

Question 16

What is a constant?

Answer 16

a variable that once defined, does not change its value

Question 17

what is the python function for returning the length of a value?

Answer 17

len()

Question 18

what is the python function for determining the position of a specified character?

Answer 18

rfind()
index = string_variablename.rfind(character)

Question 19

what is the python function for returning a substring of a given string?

Answer 19

stringvariablename[startindex:endindex]
- negative index represents the last x values in a string
-stringvariablename[-5:] returns the last five values of a string
-stringvariablename[0:-4] returns all characters except the last 4

Question 20

what is the python function for converting values into a float?

Answer 20

float()

Question 21

what is the python function for generating random numbers?

Answer 21

random.randint(a,b) (inclusive)

Question 22

what does exception handling consist of?

Answer 22

a catch block which runs in the event of an error

Question 23

What is a subroutine?

Answer 23

A named block of code design to perform a frequently used specific function

Question 24

What is an advantage of using subroutines?

Answer 24

-Avoids repetition
-code is more compact and easier to read

Question 25

What is the difference between a function and a procedure?

Answer 25

A function must return a value, whereas a procedure does not have to.

Question 26

what is the purpose of a parameter?

Answer 26

holds pieces of information to be passed to subroutines that are needed to run the process.

Question 27

What is the difference between a parameter and an argument?

Answer 27

-an argument is the actual value that is passed -a parameter is used to hold the argument

Question 28

Define a local variable

Answer 28

a variable that can only be accessed/referenced in the subroutine within which it was instantiated

Question 29

How are stack frames used during subroutine calling?

Answer 29

If a subroutine is called within another subroutine, nesting occurs. the current process taking place is pushed onto the call stack in its current state before the second subroutine is run.

Question 30

what does a recursive subroutine consist of?

Answer 30

a base case and a general case

Question 31

What are the benefits and drawbacks of using a recursive algorithm?

Answer 31

-more concise -less memory efficient -less easy to program

Question 32

what are the four basic structures of the structured approach?

Answer 32

assignment, sequence, selection and iteration

Question 33

define encapsulation

Answer 33

combining methods and procedures into a single object

Question 34

what is the result of inheritance??

Answer 34

a class inherits the attributes and methods of a parent class, while still having it's own attributes and methods (overwriting)

Question 35

describe the term polymorphism

Answer 35

-when objects are processed differently based on their class

Question 36

describe the idea of overriding in classes

Answer 36

when an inheriting class has a method of the same name with a different process or implementation

Question 37

which kind of association is the weaker kind?

Answer 37

aggregation association

Question 38

define aggregation association

Answer 38

it will still exist if the containing object is destroyed

Question 39

define composition association

Answer 39

if the containing object is destroyed, the object associated via composition association will also be destroyed

Question 40

positives of using object oriented programming?

Answer 40

-clear structure in programs -development and testing is easier -portions of code can be divided among developers -sections of code can be reused using methods like inheritance

Question 41

what are the three design principles of object oriented programming?

Answer 41

-encapsulate what varies -favour composition over inheritance -program to interfaces not implementation

Question 42

how is inheritance displayed in class diagrams?

Answer 42

an arrow pointing from the child to the parent class

Question 42

describe the design principle of 'encapsulate what varies'

Answer 42

any requirements that a likely to change in the future should be encapsulated in class for ease of access

Question 42

describe the reason for the design concept of favouring composition over inheritance

Answer 42

-composition is a more flexible relationship, though not always suitable

Question 43

what symbol represents aggregation association in class diagrams?

Answer 43

hollow diamond

Question 44

what symbol represents composition association in class diagrams?

Answer 44

a solid diamond

Question 45

what are the symbols for public private or protected in class diagrams?

Answer 45

# = protected + = public - = private # = protected