1. Algorithms and Pseudocode

2. Activity 1
Quickly sketch a flow chart for the following problem. Create a program that takes in two numbers and outputs their sum.

3. Solution Start End Store in variable “Num1” Store in variable “Num2”
Number 1?
Solution
Store in variable “Num1”
Number 2?
Store in variable “Num2”
Answer = Num1+Num2
Display Answer
End

4. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Hands up if you can explain the following:
What is an algorithm?

5. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Remembering Algorithms
In general, an 'algorithm' is the name given to a set of steps needed to complete a task.
Think of an algorithm as a recipe.
For instance you could define an algorithm to make a cup of tea. You start by filling the kettle, then place a tea bag in the cup and so on.
In computer terms, an algorithm describes the set of steps needed to carry out a software task or solve a problem

6. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Writing Algorithms
Problem
Algorithm
Algorithms are independent of any language

7. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Hands up if you can explain the following:
What is an algorithm?

8. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Writing Algorithms
Writing an algorithm in a specific language:
Too time consuming
Pointless – could just code
Can’t be taken by a programmer using a different language
Too complex – need knowledge of syntax (code specific to a language)
Writing an algorithm in everyday language (standard English):
Too time consuming
Inaccurate as it could be open to interpretation
Algorithms are independent of any language
There are therefore methods used to write algorithms so that they are succinct, accurate and easy to understand so that a programmer of any language could understand the steps required to solve a task:
Flowcharts and Pseudocode

9. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Writing Algorithms
Problem: Calculate the Sales Tax (VAT) of an item and then using it to work out the final price
1. Flowchart
2. Pseudocode
Examples of each method of algorithm writing

10. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Pseudocode
Today we will focus on Pseudocode
Represents an algorithm using adapted everyday language and common keywords from programming languages
Instructions are easy to read and understand, but look similar to statements found in programming languages and so can be more readily turned into code.
Psedo-code is NOT a strict list of commands, there are no universal standards, however, using certain keywords (as shown on the next few slides) is an expectation – this way any programmer should be able to take your algorithm an understand it.
Example:
A central heating system will try to keep the temperature between 2 values (19 and 21)
If the temperature falls below 19 It will turn the heating system on
If the temperature rises above 21 it will switch the heating system off.
START
IF Temp < 19 THEN
Heating  On
ELSE
IF Temp > 21 THEN
Heating  Off
END

11. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Start and End “Key Words”
Pseudocode begin with a START and ends with END
The algorithm goes in between.
START
……………………………..
END
Pseudocode and their statements

12. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Process “Key Words”
Most of the time pseudocode will outline the logical sequence of instructions to be carried out.
Simple processes will often use the key words shown below (like “CALCULATE X*2” or “INCREMENT X by 1)”
You don’t have to always use these words, for example the logic statements such as “Add 1 to x” or “append x to List”) are fine too..
Pseudocode and their statements
Compute
Calculate
Determine
Increment; ++ or +=
Decrement; -- or -=

13. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Input / Output “Key Words”
At times your program will most certainly ask the user for inputs and output values too.
Inputs and Outputs (like “Name?” or “…display age”) are indicated using the following words. Usually a programmer will chose one and stick with it throughout their algorithm.
Pseudocode and their statements
INPUTS:
READ
OBTAIN
GET
INPUT
OUTPUTS:
PRINT
DISPLAY
SHOW
OUTPUT

14. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Variable Assignment “Key Words”
At times your program will assign values to variables.
In pseudocode this is done using the following key words.
SET
INIT
Pseudocode and their statements
Very commonly, an arrow is used instead e.g.: X 10
This means SET X to 10

15. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Decision/Selection “Key Words”
At times your program will be programmed to make a decision based on certain conditions.
Decisions (like “IF X = 3, THEN …”) are shown using, unsurprisingly, the following key words. IF
THEN
ELSE
ELSE-IF
ENDIF
Pseudocode and their statements

16. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Loops / Iterations “Key Words”
Programs will often loop in places while certain conditions occur (infinitely) or for a set number of times (finitely).
Loops use the following key words:
Pseudocode and their statements
FINITE:
FOR
INFINITE:
WHILE / ENDWHILE
REPEAT / UNTIL

17. Algorithms and Pseudocode
Summary
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems. ,
Pseudocode and their statements
Pseudocode is written a bit like a programming language however it should never be confused with one. It is independent of any language.

18. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Pseudocode and their key words / statements in action…
GET Height
GET Base
Answer  (Base * Height) / 2
DISPLAY “Right angled triangle area” = Answer
END
1. Use of capitalised pseudocode key words/statements
2. Indentation
GET Name
FOR x = 1 TO 10
DISPLAY “Your name is” = Name
END

19. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
4 things you need to be able to do with algorithms for your exam
Understand them
Correct them if they have errors,
Complete them if they are incomplete
Produce them after being given a problem to solve

20. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Tips on reading algorithms.
Remember, arrows often show the assignment of a value to a variable. Here the variable is a list and will contain 5 items
Start from top and read each line at a time.
Remember what the key words, arrows and statements mean
Logically work out what the algorithms is doing.
Task: What is this algorithm doing?

21. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Tips on correcting algorithms.
START
WHILE TRUE
X Temperature
IF X > 19
Heating TRUE
ELSE-IF X < 21
Heating FALSE
END
Read the pseudocode and look for decisions which don’t make sense
START X
WHILE X < 10
DO X X+1
END
Or it might be a loop which you cannot get into or perhaps out of.

22. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Tips on completing algorithms.
Start from top and understand each line in turn
Remember what the keywords mean
Logically work out what the algorithms is doing.
THEN,
Use your knowledge of the algorithm so far
AND Use your knowledge of the pesudocode keywords
…and complete the algorithm
START
INPUT Length, Width, Height
objectVolume ←
Print “Volume = ”
END

23. Algorithms and Pseudocode
Learning Objectives:
(a) understand algorithms (written in pseudocode or flow diagram), explain what they do, and correct or complete them
(b) produce algorithms in pseudocode or flow diagrams to solve problems.
Tips on writing algorithms.