Topic 1 Problem Solving

Question 1

What is an algorithm?

Answer 1

A step-by-step procedure for solving a problem or carrying out a task. It is not programming code.

Question 2

Why are algorithms needed?

Answer 2

To improve efficiency by removing the need for human input.

Question 3

Describe the algorithm construct - SEQUENCE

Answer 3

Instructions provided and executed in the correct order.

Question 4

Describe the algorithm construct - SELECTION

Answer 4

Choosing which part of an algorithm to run based on a condition being true or false.

Question 5

Describe the algorithm construct - ITERATION

Answer 5

Steps in an algorithm are repeated for a set number of times, or until a condition is met.

Question 6

How might algorithms be represented?

Answer 6

Pseudo-code / Flowcharts / Structured English.

Question 7

What is Pseudo-code?

Answer 7

A way of expressing an algorithm in English, that resembles a computer language.

Question 8

What is a flowchart?

Answer 8

A diagrammatic way of representing an algorithm using symbols/text linked with arrows to show the ‘flow’ through the algorithm.

Question 9

In flowcharts, what symbol is used to represent the start/end?

Answer 9

Rounded rectangle.

Question 10

In flowcharts, what symbol is used to represent a decision/selection

Answer 10

Diamond, with two possible outcomes, Yes/No, True/False etc.

Question 11

In flowcharts, what symbol is used to represent a process?

Answer 11

Rectangle.

Question 12

In flowcharts, what symbol is used to represent control passing between other symbols?

Answer 12

Arrow.

Question 13

In flowcharts, what symbol is used to represent a subroutine?

Answer 13

Rectangle, with an extra line at both sides.

Question 14

What is a dry-run?

Answer 14

Using a pen/paper to investigate the FUNCTIONING of an algorithm.

Question 15

What is the purpose of a trace table?

Answer 15

To write down (pen/paper) the values of each variable during the execution of an algorithm.

Question 16

What is meant by a syntax error?

Answer 16

An error in the language used, eg PINT instead of PRINT

Question 17

What is meant by a logic error?

Answer 17

An error which produces an incorrect result/output. Eg Multiplies instead of divides.

Question 18

What is meant by a run-time error?

Answer 18

An error that would cause the program to crash during execution. Eg divide by zero.

Question 19

Describe the linear search algorithm.

Answer 19

An attempt to find an item in an array which starts at the beginning of the array, checks each item in turn, stops when the item is found, or the end of the array is reached.

Question 20

Describe the binary search algorithm.

Answer 20

Array must be sorted first. Select the middle value and compare with the search item. If the search item is lower, discard the middle value and the higher items to the right. If the value is higher, discard the middle value and the lower items to the left. Repeat until the search item is found, or not in the list.

Question 21

Describe the bubble sort algorithm to sort into ascending order.

Answer 21

Go through the array starting at the second item. Compare this with the value before it. If first value is higher than second value, swap the items. Repeat this until all items are in their correct place.

Question 22

Describe the merge sort algorithm.

Answer 22

An array is divided into two repeatedly until each array has only one item. The arrays are then progressively merged with the items into the correct order.

Question 23

What is meant by decomposition?

Answer 23

Breaking a large problem down into sub-problems or components. These smaller components are easier to understand and solve. Once all of the components are solved, the large problem is solved.

Question 24

What is meant by abstraction?

Answer 24

Identifying the essential elements of a real world scenario needed for use in an algorithm/program, and ignoring all non-essential elements. Eg Google Maps shows roads/names/main buildings as opposed to a photograph in Google Earth which would show every detail.