2.2 Problem solving and programming

• Describe the process of decomposition

  • Splitting a problem down
  • Into its component parts/sub-procedures/modules
• State what is meant by problem recognition

  • Identify there is a problem to be solved
  • Identifying what the problem is
• State one additional computational method.

  • Divide and conquer
  • Abstraction
  • Critical thinking
  • Modelling
  • Heuristics
  • Concurrency
  • Visualisation
  • Backtracking
• Describe the difference between passing a parameter by value and by reference.

  • By reference the function receives the memory location of the data
  • By value the function receives a copy of the variable
  • By reference will make changes to the original variable
  • By value will make changes to the copy of the variable
  • By reference will overwrite data in the original variable
  • By value will not overwrite the data in the original variable
  • By reference will keep the changes after the function ends
  • By value will not keep the changes after the function ends
• Give one benefit and one drawback of declaring the array as a global variable instead of a local variable.

  Benefits:

  • Variable doesn’t need passing as a parameter (byref)
  • You don’t need to return a value
  • Can be accessed from any function / anywhere in the program

  Drawback:

  • Increases memory usage (as it is used until full program execution is over)
  • Alterations within the function may have unwanted side effects elsewhere in the program
• Describe one feature of an Integrated Development Environment (IDE) that can be used to help write the program and one feature that can be used to help test the program

  Write:

  Auto-complete - Start typing an identifier/command and it fills in the rest

  Test:

  Breakpoints - Stop the program running at a set point to check variables
• State why performance modelling is used to test a system.

  • Simulate/model behaviour of the system (before it is) used under load
  • Because it would be too expensive/unsafe/time critical to test the real system
• State two features of any recursive algorithm

  • A function that calls itself and has a base case (that terminates the recursion)
• State the purpose of the constructor.

  To create an instance of an object from a class
• Describe what is meant by inheritance

  When the child subclass class takes on attributes/methods from parent/superclass
• Identify the stage(s) and instruction(s) run during each pipeline

  Interval 1

  • A is fetched

  Interval 2

  • A is decoded
  • B is fetched

  Interval 3

  • A is executed
  • B is decoded
  • C is fetched

  Interval 4

  • B is executed
  • C is decoded
  • D is fetched
• Explain why pipelining can improve the performance of the processor.

  • Reduces/removes latency
  • CPU is not idle while waiting for next instruction
  • Next instruction is fetched while current one is decoded/executed
  • All parts of the processor can be used at any instance in time.
• Compare two differences between recursion and iteration

  • Recursion uses more memory
  • iteration uses less memory
  • Recursion declares new variables //variables are put onto the stack each time
  • iteration reuses the same variables • Recursive can run out of memory/stack space
  • while iteration cannot run out of memory
  • Recursion can express a problem more elegantly // in fewer lines of code
  • while iteration can take more lines of code // be harder to understand Recursion will be self-referential // will call itself… • … whereas iteration does not
• Describe one difference between get methods and set methods.

  • A get method allows the attribute to be accessed / returned
  • A set method allows the attribute to be changed (with parameters)
• Barney will use an Integrated Development Environment (IDE) to debug his program code.

  Describe three features commonly found in IDEs that Barney could use to debug his program code.

  • Stepping Through The Code - to run one line at a time to see where the error is
  • Syntax Error Highlighting - to distinguish syntax errors in the program code
  • Setting breakpoints - to debug individual sections of code at a time
  • Variable watch window - To check that the variables are being updated corrected
• Discuss the benefits of using different object-oriented techniques

  • Objects can be given a different identifier by the other programs.
  • 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.
  • Encapsulation can be used by using set and get methods to ensure it is changed in a way that is intended.
  • OOP also allows programs to be easier to modify and maintain.
• Evaluate the use of data mining

  • Extracting data from databases
  • Using large data sets
  • Looking for patterns/specific occurrences of data
  • Gathering data that can be analysed and used to inform decision
  • Can identify areas to focus attention
  • Save time and money by identifying areas that are not popular/used
  • New features targeted at specific groups could bring in new business e.g. advertising
  • But care would need to be applied to privacy issues / GDPR and potential impact on the user
• Mabel has been told that true programmers write programs in a text editor, and do not use IDEs. Mabel does not agree with this statement.

  Discuss the use of an IDE in the development of this program.

  Tools to aid writing

  • Coloured font
  • Predictive text
  • Auto-correct

  Tools to aid de-bugging

  • Stepping
  • Break points
  • Variable watch window
  • Can reduce spelling errors
  • Can use to fix errors that might occur
  • Increase speed of writing
  • Fewer mistakes
  • Increase speed of testing / finding errors
  • Collaborative team working facilitate
• Explain the difference between branching and iteration.

  • Branching decides which code is run / only runs code once
  • Iteration repeatedly runs the same code in the same sequence
• State whether the parameters should be passed by value, or by reference. Justify your answer

  • By Value - the original values do not need to be modified
  • byRef would not work / would cause the routine to crash

  
• Describe the arithmetic operation of MOD. Use an example in your answer

  • Gives the remainder after division
  • E.g. 10 MOD 3 = 1
• State one benefit and one drawback of using iteration instead of recursion

  Benefit:

  • The program can/might run faster
  • Cannot run out of stack space/memory
  • Easier to trace/follow

  Drawback:

  • Iteration can lead to lengthier code
  • Iteration can lead to code that looks more complex / is harder to understand
  • Some problems are more elegantly coded with a recursive solution
• One sub-procedure will handle the user input.

  Describe three other sub-procedures Mabel could create for the given game description.

  • Select character (name, gender) - Gives the user options for choosing a character
  • Choose level - Give the user the choice of level (easy, normal, challenging) and take the user input
  • Touch enemy - Called to determine if the character touches an enemy
  • Lose life - Remove a life, if <0 then game over
  • End level - Move onto next level

  
• Describe the decision that the program will need to make within the user input sub-procedure and the result of this decision

  • Decision based on what the user has input
  • E.g. If they click left move the character left
  • if they click right move the character right
  • if they click space bar make the character jump

  
• Define pipelining and give an example of how it could be applied in the program.


  • The result from one process / procedure feeds into the next
  • E.g. the result of detecting a character touching an enemy feeds into reducing the number of lives

  
• Define the term ‘data mining’.


  • Turning large quantities of data into useful information / Finding patterns within large quantities of information
• Mary plans to use data mining to generate information about OCRRetail’s customers. Mary will use this information to benefit the company.

  Identify two pieces of information that data mining could provide OCRRetail about sales, and state how OCRRetail could make use of this information

  • Identify customer trends -To identify items to sell/offers to send customers
  • Identify which stores are making the most profit - To identify what the other stores are doing well
  • Which items are not selling well - To replace them with other items
• Define the term ‘performance modelling’


  • Simulate/test the behaviour of the system before it is used
• Identify one way performance modelling could be used to test the new system

  • Testing it with a large number of simultaneous orders (stress testing)
  • Testing it with a large number of customers/items/order
• Identify two advantages of using a visualisation such as the one shown in Fig. 3.

  • Visualisations present the information in a simpler form to understand
  • Visualisations can best explain complex situations

  
• The parameter, num1, is passed by value.

  Explain why the parameter was passed by value instead of by reference.

  • If the value is sent by value, num1 will not be overridden / it is a copy of the parameter that is used and this will produce the correct output
  • if the parameter had been passed by reference it would not produce the correct result as num1 would be overridden / because it is a pointer to the address of the variable

  
• Parameters can be used to reduce the use of global variables. Compare the use of parameters to global variables in recursive functions


  • Local variables can only be accessed within the scope of the sub-program it's defined within
  • If global, equivalent of by reference -value would be over-ridden
  • Global variable takes more memory than a local variable/parameter
  • In recursion, each call produces a new local variable for num1
  • Global would require altering the algorithm as the value would be over-ridden on each call
  • Parameter enables memory to be reallocated
• Explain why a recursive algorithm uses more memory than the iterative algorithm

  • Each recursive call stores the current state on the stack creates new variables
  • Iteration reuses the same variables
• Explain the similarities and differences between a record and a class.

  • Record is a data structure
  • A class is a template for making data structures (objects)
  • Class also has methods (which describes functionality)
  • Both store data of different types
  • Which can be accessed by their names
  • But classes can make them accessible via methods
  • Both can have multiple ‘instances’
  • Class can include visibility of properties / private

  
• The attributes in itemQueue are all declared as private.

  Explain how a private attribute improves the integrity of the data

  • Properties (are encapsulated) and can only be accessed through their methods
  • Enforce validation through the method
  • inappropriate data can be caught before entered
  • Cannot be changed/accessed accidentally
• Describe two advantages of splitting the problem into sub-procedures


  • Procedures can be re-used
  • No need to reprogram/saves time
  • Program can be split between programmers - Can specialise in their area
  • Speed up completion time - As multiple procedures worked on concurrently
  • Easy to test/debug - As each module can be tested on its own then combined.