Paper 2 all notes

• Development life cycle

  1. Analysis

  2. Design

  3. Coding

  4. Testing
• Analysis

  A process of investigation, leading to the specification of what a program is required to do
• Abstraction


  • A method used in the analysis stage of the program development life cycle; the key elements required for the solution to the problem are kept and any unnecessary details and information that are not required are discarded
• Decomposition


  • A complex problem is broken down into smaller parts, which can then be sub divided into even smaller parts that can be solved more easily
• Design

  Uses the program specification from the analysis stage to show to how the program should be developed
• Elements of design

  • Decomposition
  • Structure diagrams
  • Flowcharts
  • Pseudocode
• Coding

  The writing of the program or suite of programs
• Testing

  Systematic checks done on a program to make sure that it works under all conditions
• Top-down design

  • The decomposition of a computer system into a set of sub-systems
  • The process of breaking down into smaller sub-systems is called stepwise refinement
• Flowcharts

  A diagram that shows the steps required for a task (sub-system) and the order in which the steps are to be performed. A graphical representation used to represent an algorithm
• Pseudocode


  A simple method of showing an algorithm; it describes what the algorithm does by using English key words that are very similar to those used in a high-level programming language but without the strict syntax rules
• Structure diagrams

  A structure diagram shows the hierarchy of a system
• Benefits of Top-Down Design

  • Breaking a problem down into smaller parts/tasks make it far easier to understand, solve and manage
  • Top-down design allows several programmers or teams to work on the same project, without getting in each other's way
  • Each module of code to be tested separately
• Variable

  A storage location. It is a named value that contains data that can be changed throughout the execution
• Constant

  A storage location. It is a named location that contains a value that we don't want to change during the running of the program
• Array

  A data structure containing several elements of the same data type and stored under a single name. To reduce the number of variables used. Any item can be found using an index number
• Data Types

  • Char
  • String
  • Boolean
  • Integer
  • Real
• Algorithm

  An ordered set of steps to solve a problem
• Sequence

  The concept of one statement being executed after another
• Selection

  Decides which statements are to be executed depending upon the result of a question
• Conditional Statement

  • IF ... THEN ... ELSE
  • CASE .. OF .. OTHERWISE .. ENDCASE
• Purpose of a Conditional Statement

  • To allow different routes through a program
  • Dependent on meeting certain criteria
• Looping

  • FOR .... TO .... NEXT
  • REPEAT .... UNTIL
  • WHILE .... DO .... ENDWHILE
• Iteration

  • Count-controlled loops (FOR.. TO.. NEXT)
  • Pre-condition loops (WHILE … DO … ENDWHILE)
  • Post-condition loops (REPEAT … UNTIL)
• Subroutine

  A sub program, it is not the whole program to perform a frequently used operation with a program. That can be called when needed and reused by another program
• Procedure

  A set of programming statements grouped together under a single name that can be called to perform a task at any point in a program
• Function

  A set of programming statements grouped together under a single name that can be called to perform a task at any point in a program. In contrast to a procedure, a function will return a value back to the main program
• Parameters

  The variables that store the values of the arguments passed to a procedure or function
• Counting

  Used with repetition with the counter increased by 1 every time the loop is repeated
• Totalling

  Used with repetition with the total updated every time the loop is repeated
• Global variable

  Can be used by any part of a program – its scope covers the whole program
• Local variable

  Can only be used by the part of the program it has been declared in – its scope is restricted to that part of the program
• Syntax Error

  Occurs when a programmer does not follow the rules or structure of the language they are writing in
• Logic Error

  An error in the code that causes the program to do something it should not
• Validation

  Automated checks carried out by a program that data is reasonable before it is accepted into a computer system
• Types of Validation

  • Range check
  • Length check
  • Type check
  • Presence check
  • Format check
  • Check digit
• Verification

  Checking that data has been accurately copied from another source and input into a computer or transferred from one part of a computer system to another
• Methods of Verification

  • Double Entry
  • Visual check
• Types of Test Data

  • Normal data
  • Abnormal data
  • Extreme data
  • Boundary data
• Difference between Extreme Data and Boundary Data

  • Extreme data is the largest/smallest acceptable value
  • Boundary data is the largest/smallest acceptable value and the corresponding smallest/largest rejected value