2.1.2. Thinking Ahead

Question 1

What is the purpose of thinking ahead?

Answer 1

to make programs easy and intuitive for users to use

Question 2

What is the definition of an input?

Answer 2

data that is required to solve a problem, usually entered into the system by the user

Question 3

What is the definition of an output

Answer 3

results passed back when inputs have been processed and the problem is solved

Question 4

What 3 considerations do programmers need to make about inputs and outputs when thinking ahead?

Answer 4

1. data structures used
2. data types used
3. method of input/output (device)

Question 5

What are preconditions?

Answer 5

requirements which must be met before a program can be executed

Question 6

What 2 places can preconditions be defined?

Answer 6

within the code or documentation

Question 7

What are 2 examples of where preconditions are required?

Answer 7

1. stack functions 2. factorial function

Question 8

What 2 ways does a stack function make use of preconditions?

Answer 8

1. checks that a stack is not empty when popping an element from a stack
2. checks that a stack is not full when pushing an element onto a stack

Question 9

How does a factorial function make use of preconditions?

Answer 9

checks the number passed into the function is not negative

Question 10

What are 3 advantages of including preconditions within the documentation accompanying a subroutine?

Answer 10

1. reduces complexity of the program
2. reduces time needed to debug and maintain a large program
3. makes the subroutine more reusable

Question 11

What is the definition of caching?

Answer 11

the process of storing instructions or values in cache memory after they have been used, as they may be used again

Question 12

How is caching used in storing web pages?

Answer 12

web pages that a user frequently accesses are cached, so next time they are accessed, content can be loaded without delay

Question 13

What are 3 advantages of caching web pages?

Answer 13

1. content can be loaded without delay
2. images and text do not have to be downloaded multiple times
3. bandwidth is freed for other tasks on a network

Question 14

What is prefetching?

Answer 14

where algorithms are used to predict what instructions are likely to be be used soon

Question 15

What are 2 limitations of caching?

Answer 15

1. size of the cache
2. effectiveness of algorithms managing the cache

Question 16

What are 2 advantages of using reusable program components?

Answer 16

1. more reliable than new components as they have already been tested
2. time, money and resources are saved as developing from scratch is not required

Question 17

What are 3 examples of reuseable program components?

Answer 17

1. abstract data structures eg queues and stacks
2. classes
3. subroutines