computer science unit 2.2

sequence

• code is executed line-by-line

• from top-to-bottom

branching/selection

• block of code is run if a specific condition is met

• uses IF statements

iteration

• block of code executed a certain number of times

• or WHILE a condition is met

• uses FOR, WHILE or REPEAT UNTIL loops

2 types of iteration

• count-controlled (repeated a given no. times)

• condition controlled (until a given condition is met)

whats a variable’s scope?

• A range of STATEMENTS that a variable is VALID for

• the same IDENTIFIER to be used for different PURPOSES without CONFLICT

• the section of code

• in which the variable is available

local variables

• have a limited scope

• defined within one module

• only accessed within that module

• data is deleted once the program ends

• can be used as parameters

multiple LOCAL variables with the same name

• can exist in diff subroutines

• will not affect each other

advantages of local variables

• ensures that subroutines are self-contained

• no risk of variables being affected by outside code

global variables

• can be accessed across the whole program

• (all variables used in the main body = global)

• defined at the start of the program

• allows data to be shared by modules

advantages of global variables

• useful for values that need to be used by multiple parts of the program

• 
  

drawbacks of global variables

• could be unintentionally overwritten

• or deleted

• not deleted when program terminates, sp they require more memory than local

what if a local variable has the same name as a global

• the local variable takes precedence

whats modular programming

• a programming technique used to

• split large, complex programs

• into smaller, self-contained modules

benefits of a modular design?

• Work is easier to divide between a team

-each member knows what values go in subroutine + expected functionality

• Saves time , work in parallel

-each member can work on their area of expertise.

• Breaks problems into smaller areas.

-Easier to test/ debug/ read

-each subroutine can be tested before integration.

• Code can be reused in the project/ future projects

procedures

• a block of code which performs a specific task

• x have to return a value

• given data as parameters

functions

• block of code which performs a specific task

• must return a value

• makes use of local variables

parameter

• an item of data

• that is passed to a subroutine

• is used as a variable within the subroutine

what happens when a parameter is passed by VALUE?

• a copy of the value is passed to the subroutine

• and is discarded at the end

• so the value of og will remain unchanged

what happens when a parameter is passed by REFERENCE?

• LOCATION of data is used

• so changes may be MADE to value of original data

are changes made to the variables when passing by reference?

• yes

whats an IDE?

• a program which provides a set of tools

• used for developing programs

• and debug code

whats some features of an IDE?

• translators

• run-time environment

• error diagnostics

• code editors

• auto documentation

• syntax highlighting

• auto completion

• stepping

• breakpoint

• variable watch window

syntax highlighting

• use to check code is correct

whats stepping

• Can set the program to run line by line

• Slow down/watch execution

• Find the point where an error occurs

error diagnostics

• Locate and report errors

• give detail on errors

whats variable watch window

• allows you to view the variable/data structure

• as it runs

whats breakpoints

• Use to test the PROGRAM works UP to/at SPECIFIC points

• Check VARIABLE contents at SPECIFIC points

• Can SET a POINT where the program STOPS running

different stages of software development life cycle

1. analysis

2. design

3. development

4. testing

5. implementation

6. evaluation

7. maintenance

analysis stage?

• stakeholders state what the require in the finished product

• used to clearly define the problem and system requirements

• analyse strengths and weaknesses

• considering the kind of data involved in inputs/outputs/stored data/amount of data

design stage ?

• different aspects of new system are designed

• test plan also designed at this stage

development stage?

• splits data into individual, self-contained modules

• allocated to teams for programming

testing stage?

• alpha

• beta

• white-box

• black box

alpha testing

• carried out in-house by software dev teams

• bugs pinpointed and fixed

beta

• carried out by end-users

• feedback used for next stages

white-box

• internal structure/ design is known (to the tester)

• requires programming knowledge

black box testing

• internal structure/ design is NOT known (to the tester)

• requires limited/no programming knowledge

implementation

• software is installed onto the users’ systems

evaluation

• effectiveness of the software is evaluated against the system requirements

• different criteria are considered. like robustness reliability portability

maintenance stage?

• any errors / improvements are flagged by end-users

• programmers regularly send out software updates

  • to fix bug or security issues

waterfall cycle

• divides processes into SEQUENTIAL / structured stages

• followed in a LINEAR fashion

• Move back through processes if change required

benefits of waterfall

•