Paper 2 comp

Decomposition

-breaking down a larger program into smaller, more manageable sub programs

Abstraction

removing unnecessary information to focus on important details

Algorithmic thinking

creating step by step process to produce a solution to a problem

Flow chart symbols

line- movement

rectangle-process

rectangle with 2 vertical lines-subroutine

parallelogram-input/output

diamond-decision

oval-terminal(start and stop)

bubble sort

compare first 2 values

if in wrong order swap

compare next 2 continue until end of data set

when swaps are made repeat from start

when no swaps are made stop

-simple algorithm to program, time consuming to execute

merge sort

Split in half continuously until they are split into individual values

combine split data sets which order once merged

repeat until in one large dataset

-efficient

-may not work well for small lists

Insertion sort

take 1st value of data set,now sorted list

next value compare to previous values if,smaller put to left else stay same

repeat until all has been compared

-difficult to implement in high level/amateur programmers

-faster than bubble

linear search

looks one by one comparing to desired value

stops when value is found/or reports not found

-inefficient

-works regardless of order

binary search

picks middle value

determine whether desired is higher or lower

discards middle value and section of list value i not in

repeat until value found/reported not found

-efficient,fewer comparisons

only works when ordered

Authentication

Checking users identity

biometrics

username and password

Input validation

checks whether data matches certain rules

ensures input is sensible

can prevent SQl injection

Maintainability,easier to understand

sub-routines,easier to follow

suitable variable names, can identify purpose

comments,explain what parts of the program do

Testing

ensures program function as expected

iterative-at each stage of development

final-near end of development

test data

normal-typically expected

boundary-very edge of being valid

invalid-correct data type, outside boundaries

erroneous-incorrect data type

low level languages

binary to represent instructions

can only run on certain hardware

refer directly to hardware,programmer must understand how it works

run directly by processer

High level

English word

run on many types of hardware

abstract processor details, focus on what program needs to do

must be translated into machine code to run

compiler

translates every line of code in a program and runs after

produces executable file

run again without recompiling

executable file source code doesn’t have to be seen

ran quickly

interpreter

translates one line and reads line

no executable file

when rerun every line is retranslated

no executable file

slow

editor(ide)

modify code

auto-suggestion of key words

pretty printing(colour-coding)

auto indent

error diagnostics

find/fix errors

breakpoints stop at certain points

stepping, run code from break point one at a time

variable contents checked

runtime nvironment

run code within ide

output seen without external program

VM may be used

Translator

convert high level into machine code to be executed

compilers, interpreters