cps ias caie 2 concept

• Abstraction


  Filtering out and concentrating on the relevant information in a problem; allowing a programmer to deal with complexity
• Decomposition


  Breaking down problems into sub-problems in order to understand a process more clearly; program modules, procedures and functions all help the programmer to break down large problems
• Algorithm


  A sequence of defined steps (step by step) to solve a given problem
• Ways to represent an algorithm

  • Structured English
  • Pseudocode
  • Flowchart
• Features of good pseudocode

  • Meaningful identifier names
  • Contains comments
  • Capitalize keywords
  • Using spacing
  • Using indentation
• Identifier


  Name given to a variable in order to call it
• Variable


  A memory location that stores a value that can be changed through the execution of the program
• Constant


  A memory location that stores a value that cannot be changed through the execution of the program
• Basic data types


  • Integer
  • Real
  • Char
  • String
  • Boolean
  • Date

  
• Rules for naming identifiers

  • Should be meaningful
  • Must be unique
  • No spaces
  • Must begin with a letter
  • Consist of letters, digits and underscore
  • Must not be a reserved word
• Assignment


  A value is given a name (identifier) or the value associated with a given identifier is changed
• Sequence


  Instructions (lines of code) should be executed one after another in a fixed order
• Selection


  Construct used to decide in choosing an option from many available options based on a condition
• Selection constructs


  • IF selection
  • CASE selection
• Repetition/Iteration


  Control structure in which a group of statements is executed repeatedly
• Repetition/Iteration constructs


  • FOR loop
  • WHILE loop
  • REPEAT loop
• Rogue value


  A value used to terminate a sequence of values
• FOR loops are best used when you know the number of iterations required, and WHILE or REPEAT loops if you do not know the number of iterations required
• Situations for different loop types

  • Iterate over an array: FOR Loop
  • Reading a file into a variable: WHILE Loop
  • Asking for user input: WHILE/REPEAT Loop
  • A loop that should execute n times: FOR Loop
• Logical operations


  • Less than
  • Less than/equal
  • Greater than
  • Greater/equal
  • Equal to
  • Not equal to
• Stepwise refinement


  Process of expressing the algorithm steps of a certain task in more details steps as the modular design by splitting a problem into smaller sub-tasks, which themselves are repeatedly split into even smaller sub-tasks until each is just one element of the final program
• Subroutine


  Self-contained section of code, performing a specific task; part of the main program
• Procedure


  Performs a specific task, no value returned to part of code where called
• Function


  Performs a specific task, returns a value to part of code where called
• Procedure/function header


  • Contains the name of the procedure or function, any parameters passed to it, and, for a function, the type of the return value

  
• Argument


  The value passed to a procedure or function
• Pass by value


  A method of passing a parameter to a procedure in which the value of the variable cannot be changed by the procedure
• Pass by reference


  A method of passing a parameter to a procedure in which the value of the variable can be changed by the procedure
• Global variable


  Declared outside of the functions/procedures in a program and can be accessed by any of them
• Local variable


  Declared inside a specific function/procedure and can only be accessed by the function/procedure in which it is declared
• Benefits of using modules, procedures and functions

  • Lines of code can be re-used; don't have to be repeated
  • Can be tested/improved independently of program
  • Easy to share procedures/functions with other programs
  • Create routines that can be called like built-in commands
• Benefits of using built-in modules/library routines

  • The routines are all fully tested and should be error-free
  • No need to rewrite the many routines every single time
  • Leads to modular programming
  • Easier in maintenance
  • Saves considerable development time
• Array


  A data structure containing several elements of the same data type; these elements can be accessed using the same identifier name
• Index


  The position of each element in an array
• Array types


  • One-dimensional (1D)
  • Two-dimensional (2D)
• Pseudocode for 1D array

  1. DECLARE ArrayName[LowerBound:UpperBound]:DataType

  2. Assign values to array elements

  
• Pseudocode for 2D array

  1. DECLARE ArrayName[LowerBound1:UpperBound1, LowerBound2:UpperBound2]:DataType

  2. Assign values to array elements

  
• Bubble sort


  • An outer loop is set to stop the sort
  • A variable 'sorted' is set to 'true' at the beginning
  • An inner loop searches through the array
  • If the first number is greater than the second, they are swapped and 'sorted' is set to 'false'
  • The outer loop continues until 'sorted' remains 'true'
• Bubble sort algorithm


  1. n ← MaxIndex - 1

  2. FOR i ← 0 TO MaxIndex - 1

  3. FOR j ← 0 TO n

  4. IF MyList[j] > MyList[j + 1]

  5. THEN

  6. Temp ← MyList[j]

  7. MyList[j] ← MyList[j + 1]

  8. MyList[j + 1] ← Temp

  9. ENDIF

  10. NEXT j

  11. n ← n - 1

  12. NEXT i
• Efficient bubble sort algorithm

  1. n ← MaxIndex - 1

  2. REPEAT

  3. NoMoreSwaps ← TRUE

  4. FOR j ← 0 TO n

  5. IF MyList[j] > MyList[j + 1]

  6. THEN

  7. Temp ← MyList[j]

  8. MyList[j] ← MyList[j + 1]

  9. MyList[j + 1] ← Temp

  10. NoMoreSwaps ← FALSE

  11. ENDIF

  12. NEXT j

  13. n ← n - 1

  14. UNTIL NoMoreSwaps = TRUE