Sequences, Modules and Variables David Millard
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Sequences, Modules and Variables David Millard (demecs.soton.ac.uk) Overview Pseudocode What are Modules? Variables Parameters Pseudocode Pseudocode is a compact and informal high-level description of a computer programming algorithm that
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01
Sequences, Modules and Variables David Millard
(dem@ecs.soton.ac.uk)<br>
(dem@ecs.soton.ac.uk)<br>
02
Overview Pseudocode
What are Modules?
Variables
Parameters<br>
What are Modules?
Variables
Parameters<br>
03
Pseudocode “Pseudocode is a compact and informal high-level description of a computer programming algorithm that uses the structural conventions of some programming language, but is intended for human reading rather than machine reading”
- Wikipedia
“A notation resembling a simplified programming language, used in program design; esp. one consisting of expressions in natural language syntactically structured like a programming language”
- Oxford English Dictionary<br>
- Wikipedia
“A notation resembling a simplified programming language, used in program design; esp. one consisting of expressions in natural language syntactically structured like a programming language”
- Oxford English Dictionary<br>
04
Pseudocode “Pseudocode is a compact and informal high-level description of a computer programming algorithm that uses the structural conventions of some programming language, but is intended for human reading rather than machine reading”
- Wikipedia
“A notation resembling a simplified programming language, used in program design; esp. one consisting of expressions in natural language syntactically structured like a programming language”
- Oxford English Dictionary<br>
- Wikipedia
“A notation resembling a simplified programming language, used in program design; esp. one consisting of expressions in natural language syntactically structured like a programming language”
- Oxford English Dictionary<br>
05
Pseudocode “Pseudocode is a compact and informal high-level description of a computer programming algorithm that uses the structural conventions of some programming language, but is intended for human reading rather than machine reading”
- Wikipedia
“A notation resembling a simplified programming language, used in program design; esp. one consisting of expressions in natural language syntactically structured like a programming language”
- Oxford English Dictionary<br>
- Wikipedia
“A notation resembling a simplified programming language, used in program design; esp. one consisting of expressions in natural language syntactically structured like a programming language”
- Oxford English Dictionary<br>
06
Pseudocode “Pseudocode is a compact and informal high-level description of a computer programming algorithm that uses the structural conventions of some programming language, but is intended for human reading rather than machine reading”
- Wikipedia
“A notation resembling a simplified programming language, used in program design; esp. one consisting of expressions in natural language syntactically structured like a programming language”
- Oxford English Dictionary<br>
- Wikipedia
“A notation resembling a simplified programming language, used in program design; esp. one consisting of expressions in natural language syntactically structured like a programming language”
- Oxford English Dictionary<br>
07
Example: Making a Cup of Tea Get into small groups of 3 or 4 and write down the steps that you need to do in order to make a cup of tea
Use a sequence of simple statements like ‘Boil Water’ or ‘Put Milk in Cup’
Try and put down an appropriate level of detail so that a person could follow your instructions unambiguously
Can you group certain steps together (for example, are the first few about preparation)? Give these groups sensible names.<br>
Use a sequence of simple statements like ‘Boil Water’ or ‘Put Milk in Cup’
Try and put down an appropriate level of detail so that a person could follow your instructions unambiguously
Can you group certain steps together (for example, are the first few about preparation)? Give these groups sensible names.<br>
08
Swap with Another Group Take a look at the tea-making instructions of another group
Annotate their instructions if:
Any instruction is ambiguous
They have missed something out
They have made an assumption
They have created a group that doesn’t make sense to you
Also if they have done anything you really like :-)<br>
Annotate their instructions if:
Any instruction is ambiguous
They have missed something out
They have made an assumption
They have created a group that doesn’t make sense to you
Also if they have done anything you really like :-)<br>
09
Go Back to Your Own Instructions Take a few moments to see what they have said
Are the comments fair?
Any unexpected ones?
Would you make any changes now you have seen someone else’s instructions?<br>
Are the comments fair?
Any unexpected ones?
Would you make any changes now you have seen someone else’s instructions?<br>
10
Writing Sequences is Easy… … But getting the sequence right is hard
Often the specification is inadequate
It is easy to make assumptions without realising it
Making it complete is challenging
Making sure not to miss smaller, less-obvious steps
Creating unambiguous instructions
Machines are very unforgiving, they do exactly what you ask – nothing more, nothing less<br>
Often the specification is inadequate
It is easy to make assumptions without realising it
Making it complete is challenging
Making sure not to miss smaller, less-obvious steps
Creating unambiguous instructions
Machines are very unforgiving, they do exactly what you ask – nothing more, nothing less<br>
11
Example: Making a Cup of Tea Make a Cup of Tea
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User Pseudocode Assumptions?<br>
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User Pseudocode Assumptions?<br>
12
Example: Making a Cup of Tea Make a Cup of Tea
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User Pseudocode Assumptions:
Electric Kettle
User wants Milk and Sugar
Only making 1 cup of tea
Nothing goes wrong!<br>
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User Pseudocode Assumptions:
Electric Kettle
User wants Milk and Sugar
Only making 1 cup of tea
Nothing goes wrong!<br>
13
Modules Modules break an algorithm into logical parts (like your groups)
Helps with Clarity and Understandability
Modules can be reused
Within the same algorithm
In a different algorithm
In Programming Modules can be called:
Sub-routines (in older languages)
Functions (in procedural languages like C)
Methods (in object oriented languages like Java)<br>
Helps with Clarity and Understandability
Modules can be reused
Within the same algorithm
In a different algorithm
In Programming Modules can be called:
Sub-routines (in older languages)
Functions (in procedural languages like C)
Methods (in object oriented languages like Java)<br>
14
Example: Making a Cup of Tea Make a Cup of Tea
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
15
Fetch Utensils and Ingredients Boil Water in Kettle Make Tea in Pot Example: Making a Cup of Tea Add Tea, Milk and Sugar to Cup Make a Cup of Tea
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
16
Example: Making a Cup of Tea Make a Cup of Tea
Fetch Utensils and Ingredients
Boil Water in Kettle
Make Tea in Pot
Add Tea, Milk and Sugar to Cup
Give Cup of Tea to User Fetch Utensils and Ingredients
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Boil Water in Kettle
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Make Tea in Pot
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Add Tea, Milk and Sugar to Cup
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
Fetch Utensils and Ingredients
Boil Water in Kettle
Make Tea in Pot
Add Tea, Milk and Sugar to Cup
Give Cup of Tea to User Fetch Utensils and Ingredients
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Boil Water in Kettle
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Make Tea in Pot
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Add Tea, Milk and Sugar to Cup
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lump in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
17
Variables Variables are named items in an algorithm that can take a variable value
For example:
n_guests and n_biscuits are variables Offer guests biscuits
n_guests = the number of guests
n_biscuits = the number of biscuits they each want
Open biscuit barrel
Put (n_guest * n_biscuits) on a plate
Offer plate around<br>
For example:
n_guests and n_biscuits are variables Offer guests biscuits
n_guests = the number of guests
n_biscuits = the number of biscuits they each want
Open biscuit barrel
Put (n_guest * n_biscuits) on a plate
Offer plate around<br>
18
Parameters Parameters are variables that are passed to a module and are used inside like variables
For example:
n_guests and n_biscuits are parameters Be hospitable
Welcome 4 relations
Offer guests biscuits(4,1)
Wait for relations to leave
Welcome best friend
Offer guests biscuits(1,3)
Offer guests biscuits(n_guests, n_biscuits)
Open biscuit barrel
Put (n_guest * n_biscuits) on a plate
Offer plate around<br>
For example:
n_guests and n_biscuits are parameters Be hospitable
Welcome 4 relations
Offer guests biscuits(4,1)
Wait for relations to leave
Welcome best friend
Offer guests biscuits(1,3)
Offer guests biscuits(n_guests, n_biscuits)
Open biscuit barrel
Put (n_guest * n_biscuits) on a plate
Offer plate around<br>
19
Where are the Variables and Parameters? Make a Cup of Tea
Fetch Utensils and Ingredients
Boil Water in Kettle
Make Tea in Pot
Add Tea, Milk and Sugar to Cup
Give Cup of Tea to User Fetch Utensils and Ingredients
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Boil Water in Kettle
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Make Tea in Pot
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Add Tea, Milk and Sugar to Cup
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lumps in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
Fetch Utensils and Ingredients
Boil Water in Kettle
Make Tea in Pot
Add Tea, Milk and Sugar to Cup
Give Cup of Tea to User Fetch Utensils and Ingredients
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Boil Water in Kettle
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Make Tea in Pot
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Add Tea, Milk and Sugar to Cup
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lumps in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
20
Where are the Variables and Parameters? Make a Cup of Tea
Fetch Utensils and Ingredients
Boil Water in Kettle
Make Tea in Pot
Add Tea, Milk and Sugar to Cup
Give Cup of Tea to User Fetch Utensils and Ingredients
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Boil Water in Kettle
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Make Tea in Pot
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Add Tea, Milk and Sugar to Cup
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lumps in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
Fetch Utensils and Ingredients
Boil Water in Kettle
Make Tea in Pot
Add Tea, Milk and Sugar to Cup
Give Cup of Tea to User Fetch Utensils and Ingredients
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Boil Water in Kettle
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Make Tea in Pot
Put Tea in Pot
Put Boiling Water in Pot
Wait 2 Minutes
Add Tea, Milk and Sugar to Cup
Put Milk in Cup
Pour Tea in Cup
Put 1 Sugar Lumps in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
21
Where are the Variables and Parameters? Make a Cup of Tea
Fetch Utensils and Ingredients
Boil Water in Kettle
Make Tea in Pot (2)
Add Tea, Milk and Sugar to Cup (1)
Give Cup of Tea to User Fetch Utensils and Ingredients
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Boil Water in Kettle
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Make Tea in Pot (n_min)
Put Tea in Pot
Put Boiling Water in Pot
Wait n_min Minutes
Add Tea, Milk and Sugar to Cup (n_sugars)
Put Milk in Cup
Pour Tea in Cup
Put n_sugars Sugar Lumps in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
Fetch Utensils and Ingredients
Boil Water in Kettle
Make Tea in Pot (2)
Add Tea, Milk and Sugar to Cup (1)
Give Cup of Tea to User Fetch Utensils and Ingredients
Get Cup
Get Kettle
Get Tea
Get Milk
Get Sugar Lumps
Boil Water in Kettle
Empty Kettle
Fill Kettle with Water
Switch Kettle on
Wait until Kettle Boils
Make Tea in Pot (n_min)
Put Tea in Pot
Put Boiling Water in Pot
Wait n_min Minutes
Add Tea, Milk and Sugar to Cup (n_sugars)
Put Milk in Cup
Pour Tea in Cup
Put n_sugars Sugar Lumps in Cup
Stir Tea in Cup
Give Cup of Tea to User<br>
22
Summary Pseudocode
High level description of algorithm…
… intended for human reading…
… but structured like a programming language
Modules (subroutines/ functions/ methods)
Break down bigger algorithms into chunks
Improves Clarity and Reuse
Variables and Parameters
Are named things with a value (like in algebra)
Can make algorithms more flexible
Can also improve Reuse<br>
High level description of algorithm…
… intended for human reading…
… but structured like a programming language
Modules (subroutines/ functions/ methods)
Break down bigger algorithms into chunks
Improves Clarity and Reuse
Variables and Parameters
Are named things with a value (like in algebra)
Can make algorithms more flexible
Can also improve Reuse<br>