Component 2.2 - Algorithms And Programming Constructs

Question 1

What is an algorithm?

Answer 1

An algorithm is a set of instructions that can be used to solve a given problem

Question 2

What two things must the instructions of an algorithm be?

Answer 2

• clear

- in the correct order to produce the solution

Question 3

Algorithms are a ___ for writing a computer program to ___

Answer 3

Starting point, solve the given problem

Question 4

What programming language should an algorithm be presented in?

Answer 4

Algorithms should be presented in a way that it can be used in different programming languages. It should NOT be in computer code

Question 5

What is pseudo code?

Answer 5

Pseudo code is a way of writing instructions in plain english

Question 6

What is a flowchart?

Answer 6

A flowchart is a diagram showing the instructions to be carried out in the order they should be carried out

Question 7

What 3 things must a good algorithm be?

Answer 7

• Be finite - must not never end trying to solve a problem
• have well defined instruction (each step must be clear)
• be effective (it should give the correct result/solution)

Question 8

What does a rounded rectangle mean in a flowchart?

Answer 8

Start/stop

Question 9

What does a diamond mean in a flowchart?

Answer 9

Decision

Question 10

What does a parallelogram mean in a flowchart?

Answer 10

Input/Output

Question 11

What does a rectangle mean in a flowchart?

Answer 11

Operation

Question 12

What does a circle mean in a flowchart?

Answer 12

Connector

Question 13

What does a rectangle with two lines near each end mean in a flowchart?

Answer 13

Store/call subroutine

Question 14

What are the three basic constructs used to design algorithms?

Answer 14

Sequence, selection and iteration

Question 15

What is the sequence construct of an algorithm?

Answer 15

Algorithms consist of a series of instructions in a specific order. It is the sequence in which instructions must be carried out for the algorithm to work.

Question 16

What happens if the sequence if an algorithm is not right?

Answer 16

Computers can only follow instructions in the order they are given, if the sequence is not right the computer will still follow the order they are given in

Question 17

What is the selection construct of an algorithm?

Answer 17

A selection instruction is one where a decision must be made. This is the times in which an instruction in an algorithm may give different options

Question 18

What is the iteration construct of an algorithm?

Answer 18

Sometimes an algorithm will need a series of steps to be carried out more than once. This is called iteration, often referred to as a loop in a program. (E.g. for next loop)

Question 19

When will you use a loop with a count or rouge value?

Answer 19

You would use this when you do not know how many times you will need the instructions in the loop to be used

Question 20

How does a count value loop work?

Answer 20

Count records the-number of times a process is carried out and when it reaches the required number the loop terminates

Question 21

What is a rogue value?

Answer 21

A rogue value is a value that falls outside the range of possible values for the data that is being processed

Question 22

How does a rogue galue loop work?

Answer 22

If there is a loop asking for inputs, storing them as var which must be positive, you could input -1 for var which will end the loop (following your code)

Question 23

What does a sorting algorithm do?

Answer 23

A sorting algorithm will put items in a list into a particular order, alphabetic or numeric

Question 24

What is merge sort?

Answer 24

Merge sort is a sorting technique based on the idea of ‘divide and conquer’

Question 25

How is the idea of ‘divide and conquer’ presented in merge sort?

Answer 25

Merge sort first divides the list into two equal halves then combines them in a sorted list

Question 26

How does the merge sort algorithm work?

Answer 26

Th merge sort algorithm divides lists into two equal halves, then splits the halves into halves and so on until on,y single items are left. It then combines them in the same way they were divided but in order.

Question 27

What is bubble sort?

Answer 27

Bubble sort is a simple sorting algorithm based on the comparison of adjacent data items, swapping them if they are in the wrong order

Question 28

What is the disadvantage of bubble sort?

Answer 28

It is not suitable for large data sets

Question 29

How does bubble aort work?

Answer 29

1) Bubble sort starts by comparing the first two items in a List
2) If the first is smaller than the second it swaps them
3) It then moves onto items 2 and three and does the same
4) It keeps repeating steps 1-3 doing items 2,3 then 3,4 then 4,5 and so on
5) Once it reaches the end of the list it loops over and over again until, no swaps have been done
6) As no swaps means a sorted list

Question 30

What is linear search?

Answer 30

Linear search is a very simple searching algorithm

Question 31

How does linear search work?

Answer 31

Each item in the data set is compared with the search condition in sequence till the item is found or the end of the data set is reached. (Basically if you want to find 20, it goes through a list looking at each item one by one comparing it to 20, if it matches it has found it is successful, if it reaches the end of the list it has failed (item does not exist))

Question 32

How can the efficiency of a search be measured?

Answer 32

You can measure the efficiency of a search by considering the number of comparisons that are made before the required item is found

Question 33

Why is linear search inefficient?

Answer 33

Linear search may have to go through almost the whole list till items are found since items in the list are not ordered. It also has to go through the whole list to decide that an item doesn’t exist

Question 34

What needs to be done for a search to be more efficient?

Answer 34

For a search to be more efficient, it is necessary to sort the data into order first

Question 35

How does binary search work?

Answer 35

1) Firstly the list being searched is sorted
2) The search starts comparing the item requested to the item at the mid point
3) - If the item at the midpoint matches the search item it has been found
- If the item in the midpoint is greater than the search item all items to the right can be discarded (as they are greater)
- Opposite if it is less than
4) This process is repeated on the remaining data till the required item is found, or all items have been discarded

Question 36

If binary search calculates the midpoint with a decimal place (e.g. 6.5) what item number is taken as the midpoint?

Answer 36

The midpoint is taken as the integer part of the result (6)