thinking ahead

Question 1

how can computational problem be represented abstractly

Answer 1

input–> computational problem–> output.
INPUT: info relevant to a problem which can be passed as a parameter to a subroutine
OUTPUT: solution to the problem, which can be passed back from a subroutine

Question 2

first step in constructing a solution to computational problem

Answer 2

clear statement of inputs and outputs and name in documentation

Question 3

in order to make sure program doesn’t crash

Answer 3

specify preconditions with the DOCUMENTATION of the function eg len(list)>1

Question 4

adv of specifying preconditions

CCR

Answer 4

• specifying as part of documentation ensures user knows what Checks (if any) to carry out before calling subroutine
• no preconditions: user confident that all Checks will be performed in the subroutine, saving unnecessary Coding. makes Code easier to DEBUG AND MAINTAIN
• clear documentation of inputs/outputs/preconditions makes subroutine Reusable in different programs if in a library of subroutines

Question 5

Reusable libraries examples

Answer 5

• Windows DLL: dynamic link library- package of reusable program COMPONENTS
• programming languages have libraries of common functions eg generating random number, sqrt
• create own library

Question 6

why have own libraries

Answer 6

if have ABSTRACT data types eg queues: adding/deleting etc needed in lots of different modules so useful to have written, debugged and thoroughly tested code saving TIME

Question 7

Caching

Answer 7

temp storage of data and program instructions recently used and may be needed shortly eg last few instructions of a program for fast retrieval. done AUTOMATICALLY by operating system

Question 8

web caching

Answer 8

storage of HTML pages and images recently looked at. Gives fast access to pages recently looked at and saves using bandwidth unnecessarily as saves having to download pages again

Question 9

benefits of libraries

Answer 9

pre tested and error free
saves time as it is ready for use
written by experts
can be written in a different language