2.2.1 Programming Techniques

Question 1

What is programming

Answer 1

• Is the process of creating a set of instructions that can be executed by the computer
• There are many different programming paradigms (models), including object-oriented, procedural, functional and declarative

Question 2

What is a Sequence

Answer 2

• Sequence means that each instruction is executed once in the order given before moving onto the next Instructions = statements

Question 3

What is Branching

Answer 3

• Sequence is a vital programming construct, but there are many situations in which you wont want the computer to execute every instruction given.
• There are 3 implemetations of branching commonly available in programming languages
  
  • IF statements
  • ELIF (ELSE IF statements)
  • ELSE (IF ELSE statements)

Question 4

What are IF statements

Answer 4

• IF statements are the most basic form of branching
• They check if a condition has been met, and if it has its value is set to TRUE and the program will set execute the set of instructions

Question 5

What is IF ELSE statements

Answer 5

• Similar to IF statement but if the condition necessary is not met, the instructions within the ELSE statements are executed instead.

Question 6

What are ELIF (ELSE IF) statements

Answer 6

• This combines IF and IF ELSE statements.
• If the condition necessary to execute the instructions of IF statement, ELIF is checked

Question 7

What is SELECT CASE

Answer 7

• Another common form of selection.
• SELECT case focuses on the content of a variable and has a separate CASE for each outcome
• Another important part is CASE ELSE statement at the end of SELECT CASE. This will be executed if none other cases apply.
• Using SELECT CASE avoids the need to use multiple nested IF statements - difficult to read.

Question 8

What is Iteration

Answer 8

• Iteration is used to execute the same instruction a same number of times or until a condition is met.
• Most programming languages support 2 types: WHILE and FOR loops.

Question 9

What are FOR loops

Answer 9

• FOR loops execute an instruction a set number of times. This is count controlled. We create a count and set it to 0.
• Every time the code is executed the count is increased by 1 - when count reaches value set by programmer, the computer stops executing the code

Question 10

What are WHILE loops

Answer 10

• Are used to repeat an instruction until a condition is met - known as condition controlled loops.

Question 11

What is Nesting

Answer 11

• Is the name given to the practice of placing one construct within another.
• Example IF statement inside an IF statement

Question 12

What is Recursion

Answer 12

• A recursive function is one that repeatedly calls itself until a base case is met within a function
• Can be used to calculate factorial of a given whole number - calculated repeatedly

Question 13

What are the advantages of recursion over iteration?

Answer 13

• More natural to read (1)
• Quicker to write / less lines of code. (1)
• As some functions are naturally recursive (1) Suited to certain problems (1)
• For example those using trees (1)
• Can reduce the size of a problem with each call.

Question 14

What are examples of data types

Answer 14

• Char - A single character
• String - A series of letters and numbers
• Boolean - Either TRUE or FALSE
• Integer - A whole number
• Float - A decimal number

Question 15

What is a Variable

Answer 15

• Identifier/name of a …
• Memory location used to store data

Question 16

What is Modularity

Answer 16

• When a sequence of instructions is going to be repeated a numberat different points, it is useful to put them in a separate subroutine - this can be called at relevant points - code is easier to maintain, less eror prone and easy to modify.

Question 17

What are Local Variables

Answer 17

• Defined within one module…
• … accessible only in that module
• Can be used as parameters
• Data is lost at end of module
• Can overwrite global variables (with the same name)

Question 18

What are Global Variables

Answer 18

• Global Variables are available throughout the program to any subroutine.
• Where in a program a variable can be accessed is called the scope. It is good practuce to limit the scope of many variables - this is to aid maintainability and code reuse.
• Global variables should be declared at the start of the program after any imported libraries

Question 19

What is a subroutine

Answer 19

• A subroutine is defined as a named block of code that carries out a specific task.
• Most programming languages make use of 2 types of subroutine: functions and procedures

Question 20

What is a function

Answer 20

• A function is a named section of program (1) that performs a specific task (1). It returns a value (1), it is often called inline (1).

Question 21

What is a procedure

Answer 21

• Procedures are subroutines that dont return a value
• They can display information to a user but dont return any information back to the main program.

Question 22

What is passing parameters by value

Answer 22

• Parameters can be used to pass values into a subroutine..
• Example procArea (x,y) replaces the word height with a copy of the value stored in x. 42 is displayed
• Parameters should be used in preference to global variables as they can be easier to read and maintain

Question 23

What is passing parameters by reference

Answer 23

• An alternative way of passing parameters into subroutines is to pass by reference rather than making a copy of the variable, the subroutine is passed the address of the variable .
• The main difference is that any change made within the subroutine will also affect the variable outside the subroutine.

Question 24

What are IDEs

Answer 24

• Integrated development environment
• A (single) program (1) used for developing programs (1) made from a number of components (1)
• IDEs come with a range of tools for helping programmers debug their code, including automatic error checking, error reports, breakpoints and stepping through.

Question 25

What are breakpoints

Answer 25

• Breakpoints allow the programmer to pause the program at a specific point in its execution and look at the contents of variables to diagnose logic problems that are impossible for IDE to diagnose.
• This will halt the execution there and help the programmer spot the problem.

Question 26

What is stepping through

Answer 26

• Stepping through allows the programmer to place a breakpoint that pauses the execution then click “step into” to execute the next instruction in the sequence, pausing before clicking “step into” again to repeat the process.
• Equivalent of having a breakpoint placed on every line in your program
• Once the execution has been paused, the programmer clicks “step into” to execute the next instruction, check contents of variables and “step into”

Question 27

Exam Question: Identify and explain 3 features commonly found in IDEs that help programmers debug their code (6)

Answer 27

• Debugging tools allow inspection of variable values
  
  • this can allow run-time detection of errors
• Code can be examined as it is running
  
  • which allows logical errors to be pinpointed
• IDE debugging can produce a crash dump
  
  • which shows the state of variables at the point where an error occurs
• It can display stack contents
  
  • which show the sequencing through procedures / modules
• It can step through code
  
  • which allows the programmer to watch the effects each line of code
• The insertion of a break-point
  
  • allows the program to be stopped at a predetermined point in order to inspect its state

Question 28

Exam Question: Describe a difference between a local and global variable (2)

Answer 28

• Global variable is visible throughout a program / may be accessed from more than one part of the program (1), local variable is visible only in module / construct where it is created / declared (1)

Question 29

Exam Question: Explain using an example why global variables are used (

Answer 29

• A global variable used where a value needs to be accessible from various parts of a program
• it is the same value
• Irrespective of the place where it is accessed
• Any sensible example of a value that will reasonably need to be the same, e.g. today’s date, VAT rate, pi (1 – AO 2.1).

Question 30

Exam Question: Explain why good programming practice generally avoids the use of global variables (2)

Answer 30

• Global variables make it difficult to integrate modules (1)
• they increase complexity of a program (1)
• they may cause conflicts with names written by others / in other modules (1)
• they may be changed inadvertently when program is complex (1).

Question 31

Exam Question: Explain why parameter passing is better than global variables (2)

Answer 31

• When a parameter is passed to a function, only a copy of the data passed may be changed (1)
• therefore no unforeseen effects will occur in other modules (1).
• This is the case only if passed by value (1).

Question 32

Exam Question: Compare a program procedure with a function (2)

Answer 32

• A procedure is also a sub-section of a program (that performs a specific task) (1)
• but it does not necessarily return a value (1).
• Most programming languages nowadays use functions (1).

Question 33

Exam Question: What are the disadvantages of using recursion over iteration

Answer 33

• Can run out of stack space / memory (1)
• (due to too many calls (1))
• causing it to crash (1)
• More difficult to trace / follow (1)
• as each frame on the stack has its own set of variables (1)
• Requires more memory than the equivalent iterative algorithm.
• Usually slower than iterative methods (1)
• due to maintainence of the stack (1)

Question 34

Exam Question: Describe 2 features of global variables that distinguish them from local variables

Answer 34

• Defined at start of program
• Exists throughout program / in all modules
• Allows data to be shared by modules

Question 35

Discuss the different object oriented techniques that Barney could use

Answer 35

• Encapsulation set and get methods to ensure that the nodes in the linked list are changed in a way that is intended.
• A class can be used to declare the attributes and methods for the linked list. These will initialise the nodes.
• Objects can then be used be used to instantiate the class each time a new linked list is needed.
• Further subclasses may be used by other programs. These can therefore take on the attributes and methods from the base class. These can also be changed or overridden depending on the purpose of the other programs

Question 35

Discuss the different object oriented techniques that Barney could use

Answer 35

• Encapsulation set and get methods to ensure that the nodes in the linked list are changed in a way that is intended.
• A class can be used to declare the attributes and methods for the linked list. These will initialise the nodes.
• Objects can then be used be used to instantiate the class each time a new linked list is needed.
• Further subclasses may be used by other programs. These can therefore take on the attributes and methods from the base class. These can also be changed or overridden depending on the purpose of the other programs

Question 36

Why would using OOP techniques be good?

Answer 36

• Code reusability
• His linked list can be saved as library and then reused many times leading to less code.
• OOP also allows programs to be easier to modify and maintain.