2.3 Producing Robust Programs

Question 1

What does input validation do?

Answer 1

Input Validation is checking data input by the user meets specific criteria / rules before processing.

Question 2

Why do we use Input validation?

Answer 2

By using Input validation the program is more:

• Robust
• User Friendly
• Prevent Errors occurring later in the algorithm

Question 3

What are the types of checks

Answer 3

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• Type Check
• *Check whether data is the right type**
• Range Check
• *In data in the correct range. E.g. 1- 10**
• Presence Check
• *Is the data actually there. It rejects blank inputes**
• Format Check
• *Is the data in the right format. E.g. dd/mm/yy**
• Length Check
• *Is it the right length. E.g. Password is too short or too long**

Question 4

What are some of the issues you have to anticipate?

Answer 4

• Dividing by Zero.
• Communication Error
• Printer or Peripheral Error
• Disk Error

Robust programs will handle all these situations by checking files and data before attempting to use them for further processing.

Question 5

How is Dividing by 0 a problem?

Answer 5

In mathematics, there is no number which when multiplied by zero returns a non-zero number. Therefore the ALU cannot compute a division by zero.

Question 6

How is Communication error a problem?

Answer 6

Online systems require connections to host servers.

If this connection is dropped, unable to be established or the server is overloaded,

it could potentially cause a program to crash or hang when loading/saving data.

Question 7

How is Peripheral error a problem?

Answer 7

Any peripheral may be in an error mode (e.g. paper jam)

Question 8

How is Disk error a problem?

Answer 8

Programs that read and write to files must handle exceptions, including:

• The file/folder not being found.
• The disk being out of space.
• The data in the file being corrupt.
• The end of the file being reached

Question 9

What is Authentication?

What are the ways it can be achieved?

Answer 9

• Authentication is the process of a user confirming that they are who they say they are on a computer system.

This can be achieved with:

• Username and password to access systems
• Recovering a password requiring clicking on a link within the email that is sent to the registered address
• Encryption of data files
• Check for human and not bot attempting access (e.g. reCAPTCHA)

The factors of authentication can be broken down into three main groups:

something you are - username, bank account number, or anything that identifies the user uniquely
something you know - password, pin, secret answer to a question
something you have - swipe card, biometrics

• Programmers should also be aware of the potential for SQL injection hacks and other used by hackers.

Question 10

How can you increase Maintainability of a program? wcidpc

Answer 10

Comments, white space, indentation, variable names, procedures and constants

• Use Comments to Explain the purpose of program & sections of code. Typically selections, iterations and procedures. They can also explain unusual approaches.
• Use white space to make sections of a program easier to read as it stands out more
• Use Indentation for selection and iteration allows the programmer to easily see which code falls within the selection or iteration, and where it ends.
• Use descriptive variable names and explain their purpose with a comment when declared.
• User procedures and/or function to Structure the code & Eliminate duplicating portions
  ​
• Use constants declared at the top of the program.

Question 11

Why do we test our program?

Answer 11

• To ensure there are no errors(bugs) in the code.
• To check that the program has an acceptable performance and usability
• To ensure that the unauthorised access is prevented
• To check the program meets the requirements

Question 12

What is iterative testing?

Answer 12

Performed whilst the software is being developed

• Each new module is tested as it is written.
• Program branches are checked for functionality.
• Checking new modules do not introduce new errors I not existing
  code.
• Tests to ensure the program handles erroneous data and
  exceptional situations.

Question 13

What is terminal testing?

Answer 13

Performed when the program is finished

• Testing that all modules work together (integration testing)
• Testing the program produces the require results with normal, boundary, invalid and erroneous data.
• Checking the program meetings the requirements with real data.

Question 14

What are Syntax errors

Answer 14

• The rules of the language have been broken
• The program will not run (Compiled languages)

Syntax errors happen because:

• Variables are not declared or initialised before use
• Incompatibility of variables types e.g. total = “A”
• Using assignments incorrectly
• Keywords misspelt

Question 15

What are logic errors and why do logic errors happen

Answer 15

The programs run but does not give expected output

Logic errors can happen because:

• Conditions and arithmetic operations are wrong
• Sequence of commands is wrong
• Division by zero
• Exceptions

Question 16

What are normal inputs?

Answer 16

Data which should be accepted by a program without causing Errors.

Question 17

What are boundary/extreme inputs?

Answer 17

Boundary - Data of the correct type which is on the edge of accepted validation boundaries.

Question 18

What are invalid inputs?

Answer 18

invalid is Data of the correct type but outside accepted validation checks.

Question 19

What are erroneous inputs?

Answer 19

Erroneus Data of the incorrect type which should be rejected by a computer system.

This include no input being give when one is expected.

Question 20

How do you refine algorithms to make them robust?

Answer 20

• Code should anticipate all inputs and it should deal with ‘bad’ data, or missing data, and not crash.
• It should ensure prompts to the user are helpful and that the input can only be of the correct type

Question 21

What are structure diagrams and their benifits?

Answer 21

Question 22

What is defensive design?

Answer 22

Defensive design considerations

Defensive design is contingency planning using validation, sanitisation, authentication, maintenance and testing.

The purpose of defensive design is to ensure that a program runs correctly and continues to run no matter what actions a user takes. This is done through planning for all possibilities (contingencies) and thinking about what a user may do that the program does not expect.

Defensive design encompasses three areas:

• protection against unexpected user inputs or actions, such as a user entering a letter where a number was expected
• maintainability - ensuring code is readable and understandable
• minimising/removing bug

Question 23

Why do we Test?

Answer 23

• To ensure there are no errors (bugs) in the code.
• To check that the program has an acceptable performance and
usability.
• To ensure that unauthorised access is prevented.
• To check the program meets the requirements