Paper 2

• Abstraction

  removes unnecessary details from a problem in order to solve it

  allows us to separate the ‘logical’ from the ‘physical’

  e.g. the London Tube map, only know what stations are on the line, not the distance or which direction
• Decomposition


  involves the breaking down of a problem into smaller, simpler steps or stages

  use structure diagram to break it down

  Each box can be further subdivided until each box represents a single, simple subtask

  when tasks broken down / decomposed, it is easier to solve the problem
• Pseudocode

  code written down

  better to write indents
• Syntax error


  spell incorrectly, missing correct punctuation
• Logical Error


  code will not work how programmer intended
• High level Programming


  Python, Visual Basic, C#, Java
• Low Level Programming Language

  Assembly Language
• Binary Search:

  • happens only if the list is sorted
  • more efficient than linear search
  • works by repeatedly dividing in half the portion of the data list that could contain the required data item
  • Continued until there is only 1 left in the list
• Linear Search


  • when data unsorted
  • start at beginning and look through every item
• DIV (// in python)

  • an integer division
  • works like normal division but returns the whole number (no decimal)
• MOD (% in python)

  gives the remainder of integer division
• Sequence

  • the statements are executed one by one in the order they are written
  • all programs have a series of steps to be followed in sequence
  • Sequence may be a series of calls to different subroutines which perform different tasks
• Selection

  • an IF statement is a type of selection statement
  • the next statement to be executed depends on whether the condition being tested is TRUE or FALSE
• Iteration


  means repetition
• Iteration statements


  • for … next
  • while … endwhile
  • do … until
• Boolean Operators AND

  AND - semi circle shaped diagram

  
• Boolean Operators OR

  OR - deformed triangle shape

  
• Boolean Operators NOT

  NOT - triangle shaped

  
• Data Types

  Integer

  Real/Float

  Boolean

  Character

  String

  Casting
• Integer

  a whole number (3, 45, -453)
• Real/float


  a number with decimal (34.456, -9.234, 4.0)
• Boolean

  has the value TRUE or FALSE
• Character


  • a single character
  • any letter, digit, punctuation mark or symbol that can be typed
• String

  • 0 or more characters
  • can be null (empty), just one character or several characters
• Casting

  • changing the type of variable value from one type to another
  • using functions such as int(), float() or str()
• Types of string Manipulation

  length of string

  substring

  convert cases

  find position of a character or the start of string
• length of string


  stringname.length
• substring


  stringname.substring(StartingPosition, numberOfCharacters)
• convert cases


  • stringname.upper
  • stringname.lower
• find position of a character or the start of string

  stringname.index()
• SQL Key Words

  SELECT

  WHERE

  FROM
• Example of how to use SQL

  SELECT FirstName, Surname

  FROM members

  WHERE Town = 'Ipswich'

  
• 1-dimensional Array

  • first element of array has a subscript of 0, e.g. 3rd box is 2
  • Individual boxes can be used just like variables
  • Can assign, input and output values to them
• 2-dimensional arrays


  a collection of data elements arranged in a grid-like structure with rows and columns
• Anticipating Misuse

  programmer must try to make sure that whatever a user enters when they run a program, it will not crash or give incorrect result
• Authentication Routines

  optical, facial or fingerprint recognition
• Input Validation

  Range Check

  Type Check

  Length Check

  Presence Check

  Format Check
• Range Check


  a number of date is within a sensible/allowed range
• Type Check

  data is the right type such as an integer or a letter or text
• Length Check

  text entered is not too long/short → password greater than 8 but less than 25