Computing Paper 2

• How can algorithms be represented?

  Via pseudocode or flowcharts
• What is abstraction and decomposition?

  Abstraction removes unnecessary detail from a problem.

  Decomposition breaks a problem into sub-problems that each represent a specific task
• What does this symbol represent in a flowchart?

  Start/End

  
• What does this symbol represent in a flowchart?

  Process

  
• What does this symbol represent in a flowchart?

  Choice

  
• What does this symbol represent in a flowchart?

  Input/Output

  
• What does this symbol represent in a flowchart?

  Subprogram

  
• What does this symbol represent in a flowchart?

  Direction of flow

  
• What are tracetables?


  A table that shows how value changes when an algorithm is carried out. They go through each line of code and only add to a column when that column's value changes. Gaps are fine.
• How does a linear search work?

  Compares each item one by one until target is found.

  Pros: No need for list to be in order

  Cons: Can be slow as each item may need to be checked
• How does a binary search work?


  • Compares middle item to its target
  • Discards the half of the list which the target cannot be in
  • Finds next middle item and repeats until target is found

  Pros: Halves search space, making it more time efficient than linear search

  Cons: Array must be sorted first
• How does a bubble sort work?

  • Look at first two items in list, if they're in right order you don't have to do anything. If they're in the wrong order, swap them
  • Move onto next pair of items until you get to end of list - this is called one pass
  • Repeat steps until no more swaps in a pass

  Pros: Simple algorithm and does not use much memory

  Cons: Inefficient way to sort a list and does not cope well with a large list of items
• How does a merge sort work?

  • Divides list into two parts continuously until each item has 1 item
  • Then combines the two lists at a time, keeping items in order

  Pros: More efficient and quicker than bubble sort for large lists and has a consistent running time

  Cons: Slow for small lists and uses more memory
• How does a insertion sort work?

  • Starts with one item in the "sorted" part and moves items one by one from the "unsorted" part to the "sorted" part

  Pros: Copes very well with small lists and is very quick to add and check items in an ordered list

  Cons: Does not cope well with large lists
• What data types are there?


  Integer - A whole number

  Real/Float - A number with a fractional part

  Boolean - True or false

  Character - A letter, number or symbol

  String - A group of characters
• What arithmetic operators are there?

  Multiplication - *

  Exponentiation - ^

  Division - /

  Quotient - DIV (cuts of decimal)

  Modulus - MOD (shows remainder only)
• What comparison operators are there?

  Equal to: ==

  Not equal to: !=

  Greater than: >

  Less than: <

  Greater than or equal to: >=

  Less than or equal to: <=
• What boolean operators are there?

  NOT - opposite

  AND - both sides needed

  OR - Only one side needed
• What is a variable and a constant?

  Variable - identifiers that hold a value that can be changed (variable = "value1")

  Constant - identifiers that hold a value that cannot be changed (const PI = 3.142)
• What is selection?

  Where IF statements are always checked

  • ELSE IFs or ELIFs are only checked if previous conditions were false
  • ELSEs have no conditions and only run if all previous conditions were false
  • SWITCH statements are useful where a variable determines the selection
• What is iteration?

  Count-controlled loops

  • FOR loops repeat a set number of times

  For example:

  For i in range(5)
• What are condition-controlled loops?

  Where loops are repeated until a condition is broken.

  • WHILE loops repeat until a condition is broken
  • DO UNTIL loops repeat until a condition is met
• What is a data structure?

  Organised collections of items.

  An array is an example
• What is an array?

  A data structure that contains items of the same data type and is of a fixed length

  • Assume the index starts at 0 unless told otherwise
• What is SQL?

  Structured Query Language, used to search and retrieve data

  SELECT Field(s)

  FROM Table

  WHERE Condition
• What are 2D arrays?

  Data structure that represents fields and records
• How do we read & write a file?

  • Before reading or writing to an external file we need to open it.

  textFile = open ("client_data.txt")

  textFile.writeLine ("AJ, 24, London")

  while NOT textFile.endOfline()

  print(myFile.readLine() )

  endwhile

  
  

  textFile.close()

  • and when your done, you need to close it
• What are sub programs?

  Named out line of blocks of code that you must call to execute them.
• How can we make a code more maintable?

  • Built from many sub programs
  • Consistent in indentation
  • Consistent in naming conventions
  • Uses comments to explain code (#)
• What is the point of robust programs?

  It makes it so your program won't crash, won't have errors and will be reliable.
• What is the point of defensive design aims?

  To make programs robust because users can't be trusted so anticipate misuse.
• What are the two types of testing?

  Iterative:

  Testing of modules throughout development. Any issues found will be fixed and the module should be retested

  Terminal:

  Testing of the whole program at the end of development
• What are the two types of errors?

  Syntax - not following rules of the language so code won't run

  Logic error - code runs but not as you intended
• What is validation?

  Enforcing a rule around user input
• What is authentication?

  Checking the identity of a user through password checks etc
• How can we test data for robustness?

  Normal - typical user inputs

  Boundary - on the edge of being allowed

  Invalid/Erroneous - completely wrong
• What is this logic gate?

  NOT

  • Reverse logic state e.g. if input is true, output will be false

  
• What is this logic gate?

  AND

  • If both inputs are true, then the output is true

  
• What logic gate is this?

  OR gate

  • If both inputs are false, output is false otherwise outputs are true

  
• What are truth tables?

  Logical tables showing all possible inputs of and associated outputs for each input