Computer science 2.1

• Abstraction

  The process of removing unnecessary details and including only the relevant details.Part of computational thinking and focusses on what is important in problem solving.
• Decomposition

  Breaking a complex problem down into smaller more manageable parts.As dealing with many different stages of a problem at once is more difficult than breaking a complex problem down into smaller more manageable parts and solving each problem at a time
• Algorithmic thinking

  A way of getting to a solution by identifying the individual steps needed.By creating a set of rules an algorithm that is followed precisely ,leads to an answer.Algorithmic thinking allows solution to be automated.Eg learn algorithms for multiplication if algorithm is followed then you can get the answer.
• How to do Algorithmic thinking

  Break problem down

  Thinking about what data is important and not

  Thinking about relevant data structures

  Tackle each part of the program step by step
• What to think about when tackling a problem

  inputs, processes and outputs
• Inputs

  Anything that needs to be supplied to the program so it can meet its goals.

  Often input by user

  Appropriate variable name and data type for the input
• Processes

  Consider what calculations need to be performed while the program is running.

  Does data need to change formats or data types
• Outputs

  Consider what your program needs to output

  Consider form output needs to take

  Consider appropriate variable name and data type for any output
• Structure diagrams

  A method of designing a solution to a problem.

  Structure diagrams illustrate problem decomposition.Can be used for developers to understand a problem to code and to share with users during system analysis.Produced using step-wise refinement.Break problem down using decomposition.The lowest level nodes should achieve a single task.They can then be coded as a single module or sub-program
• Pseudocode

  An alternative, text-based way of representing the sequences of steps in an algorithm. Pseudocode can be thought of as a simplified form of programming code.
• What does the prefix pseudo mean?

  False or not genuine
• oval symbol flowchart

  start/stop
• parallelogram symbol flowchart

  input/output
• rectangle symbol flowchart

  process
• rectangle with lines flowchart

  sub routine
• diamond symbol flowchart

  decision
• Flowchart


  Symbols

  
• coment

  //
• Input

  Variable=input(prompt)
• variables

  Assignment

  Constants

  Global variables
• Assignment

  x=3
• constants

  const vat =20
• global variables

  global userid=123
• Casting

  str(3) returns 3

  int("3") returns 3

  float("3.14")returns 3.14

  real("4.52")returns 4.52

  bool("True")returnsTRUE
• Outputs

  Print("hello")

  prints(variable)
• for loop

  for i = 0 to 7

  ........

  next i
• while loop

  while answer!=x

  ........

  endwhile
• do while loop


  do

  ...................

  until answer==x
• Comments 


  AND

  OR

  NOT
• OCR EXAM LANGUAGE

  
• OCR EXAM LANGUAGE P2

  
• If-Then-Else


  If x==6 then

  ......

  else if...then

  .........

  else

  ..........

  endif
• case select or switch

  Switch x:

  case "a":

  ......

  case "b":

  .......

  default:

  .......

  Endswitch
• string length

  variable.length
• substrings

  variable.substring(start ,num)
• uppercase

  variable.upper
• lowercase

  variable.lower
• ASCII conversation


  ASC(character)

  CHR(ascii number)
• procedure

  Procedure name (...)

  .....

  Endprocedure
• calling a procedure

  procedure(parameters)