F452 Writing maintainable programs.

1. Define the following terms:

• Variable [1]
• Constant [1]
• Reserved word [1]

A variable is a named area of memory of a specific data type that can be changed during the running of the program.

A constant is a named area of memory of a specific data type that doesn't change during the running of the program.

A reserved word is an example of a bad identifier name, they are pre existing words in a programming language.

2. Discuss the need for good programing techniques to facilitate the on going maintenance of programs.  [8]

• Easily understandable identifier names and comments.
• Appropriately positioned scopes for constants and variables.
• Consistent/ meaningful identifiers.
• Well laid out, eg comments, separated blocks.
• To help others understand your code.
• To help others build on your code.
• Functional decomposition (self containing parts of the code by 'encapsulating' them).

The Webernet.

• The internet is a wire. (could be fibreoptic)
• 2 computers connected directly using this wire are connected
• Every computer has its ow unique addresses : IP addresses.
• We associate domain names with IP addresses. "we're only human."-Human Humanson.
• Files stored on a server on some computer somewhere.
• Domain Name Service (DNS) : allows you to find domain names and their IP addresses.
• Computer indirectly connected to the internet are known as clients.
• To look at the internet: Client goes through DSL to ISP
• Computers break sent pictures into smaller chunks, called 'packets'.
• Routers help direct packets to where they need to go.
• Every time a packet goes through a router it gets IP code added to the address so that it can be returned through the same servers.
• The packet size is generally 1kB each (1000 or 1024 bytes)

F452 - String manipulation (c#)

MODULUS:

MOD or % 

the remainder when dividing one number by another

e.g 7 MOD 3 = 1

DIV 

the whole number result

e.g 47 DIV 10 = 4

\r end of line.

\n new line.

Concatenation:

string.Concat(string, "part being added");

Replace:
string.Replace(string, "New string.\n");

Format:

string,Format("{0}: {1:0,0} - {2:yyyy}");

Turning stuff into strings:

datatype.ToString();

Turning strings into integers:

//CAUTION; HANDLE WITH CARE 

(characters cannot be converted)//

int.Parse(text);

{ A = 1, B = 1 }

AND

&&

e.g IF ((A==2)&&(B==3))

Returns FALSE or 0

OR

||

e.g IF ((A==2)||(B==3))

Returns False or 0

NOT

!

e.g IF (!(A==2))

Returns True or 1

Concatenation

Means joining one or more strings together.

Replace

Lets you replace a given char in a string with another character.

Extract

Returns part of the strings from between two specified elements.

Length

Returns the number of characters in a string.

charCodeAt

Returns the ASCII value of a given element.

SWAP

Swaps two given chars.

HANDY FACTOID:

In ASCII the char A is given the code 65.

Validation:

Presence check:

Is the data present, has the required field been completed?

Length check:

Is the data a suitable length?

Format check:

Correct format? e.g dd/mm/yyyy

Range check:

Is the data in the correct range.

Existence check:

Does the data match something that already exists in the system?

F452 - Development.

Writing bad code is easy; writing good code is difficult; writing really good code is REALLY difficult.

What’s a bug?

A bug is where the software (or system) does something unexpected or undesirable.

Not all bugs are accidents though.

Types of bugs:

• Functional: (car will not start)
• Non functional: (the car travels extremely slowly)
• Reproducible:
• Non-reproducible:

[All software has bugs.]

How to write good code:

• Easy to read (Notation).
• Robust/ functional.
• Proceeded by planning.
• Comments.
• Well formatted, readable code.
• Error handling.
• Documentation.
• “Brain sized” chunks.
• Well tested code.
• Understandable by others.

What do you need to design software?

• Brain.
• Pen and paper.

{NO computers, mood room or IDE.}

You CAN (not) do everything.

• Use teams of people to split up work.
• Use software tools to make the interaction easier.

Humans suck at doing stuff; computers suck at designing.

Tools for software development:

• API’s 

[Application Programming Interface](Library of code for use).

• Source control 

(controls additions to the source code, updates everyone's)(versioning; checking in-&-out; branching).

• Build tools 

[compiler] (brings the code together for execution; turns a high level language into machine code)

• Artifact control 

(keeps a compiled copy).

• Documentation.
• Bug tracking software.

(Prioritises issues and assigns tasks to correct the code; links with versioning)

• Automated testing.

• Continuous integration servers/ automated build tools 

(keeps track of everyone's addition and brings it together)

• Automated deployment 

(,e.g: ios distribution).

Software development lifecycles:

Waterfall (traditional):

• Requirements.
• Design.
• Code.
• Test.
• Deploy.
• Support.
• End of life.

Agile (the upstart):

Rough requirement.

Build something that works.

(but that is fully functional).

Refine the requirements.

Build something that works a bit better.

The computer does the testing.

“If the test fails give me a ring; if the test works don’t bother me.”

!xiety (Bangxiety) meter:

• Designed to tell the user when the battery is going to run out.
• Every system has inputs and outputs, even this piece of tech.

Some of the design challenges:

• Reading the wheel speed.
• Recording how much power the batter has used.
• Key presses.

Knowledge based system answers

The three parts of a knowledge based system include:

•          Collecting information from the user. (knowledge based)
•          Returning  applicable information. (inference engine)
•         Checking to see if the result is acceptable.  
•      Stores data.(raw based)

For a doctor’s office help desk:

Information would be collected about the patient’s condition. The system would suggest a possible answer then check with the patient whether their results are legible or applicable to their situation.

A help desk could also use a knowledge based system to simply check appointments by having the user input their name or other patient information then receive an appointment time or doctor's information.