Design, Testing and Translators

Question 1

What is structured programming?

Answer 1

Structured programming decomposes the program that you want to write into manageable modules. Each of these modules is then decomposed even further into smaller modules and eventually into modules that perform individual tasks

Question 2

Give some advantages of using structured programming.

Answer 2

1) coding is easier because you’re only writing subroutines that carry out very simple tasks
2) lots of programmers can work on one program as each module can be written independently
3) it’s easier to test structured programs as each module can be tested individually
4) individual subroutines and modules can be fixed and updated without affecting the rest of the program
5) you will be able to reuse the subroutines and modules in programs you write in the future

Question 3

Give some features of maintainable source code.

Answer 3

1) comments are useful for explaining what the key features of a program do
2) indentation can be used to separate different statements in a program
3) variables, subroutines and parameters should be named so that they refer to what they actually are
4) only use global variables when necessary as they could affect the rest of your code

Question 4

What is authentication?

Answer 4

Authentication can confirm the identity of a user before they’re allowed to access certain pieces of data or features of the program

Question 5

Why is authentication used?

Answer 5

Authentication is used to improve security

Question 6

What can be done to make a password-based authentication system more secure?

Answer 6

1) force users to use strong passwords and get them to change their passwords regularly
2) limit the number of failed authentication techniques before access to an account is lost
3) ask for a random selection of characters from the password on each authentication

Question 7

Define the term ‘input validation’.

Answer 7

Checking if data meets certain criteria before passing it into the program

Question 8

Give some input validation checks.

Answer 8

1) range check
2) presence check
3) format check
4) look-up table
5) length check

Question 9

Define the term ‘syntax error’.

Answer 9

When the compiler or interpreter doesn’t understand something you’ve typed because it doesn’t follow the rules or grammar of the programming language

Question 10

Define the term ‘logic error’.

Answer 10

When the compiler or interpreter is able to run the program but the program does something unexected

Question 11

Why are logic errors more difficult to diagnose than syntax errors?

Answer 11

Compilers and interpreters won’t pick them up

Question 12

What are the three different types of test data?

Answer 12

1) normal (typical) data
2) boundary (extreme) data
3) erroneous data

Question 13

What are trace tables used for?

Answer 13

Dry running a subroutine or algorithm to make sure there are no logic errors

Question 14

What is time efficiency?

Answer 14

The amount of time it takes an algorithm to complete a task

Question 15

Define ‘machine code’.

Answer 15

Low-level code that represents how computer hardware and CPUs understand instructions. It is represented by binary numbers

Question 16

Define ‘assembly language’.

Answer 16

Low-level programming language closely related to machine code

Question 17

Give an example of machine code.

Answer 17

000000 00010 00011 00100 00000 100000

Question 18

Give an example of assembly language.

Answer 18

ADD r4, r3, r3

Question 19

Give some characteristics of high-level languages.

Answer 19

1) one instruction represents many instructions of machine code
2) the same code will work for many different machines and processors
3) the programmer can easily store data in lots of different structures without knowing about the memory structure
4) code is easy to read, understand and modify
5) must be translated into machine code before a computer is able to understand it
6) you don’t have much control over what the CPU actually does so programs will be less memory efficient and slower

Question 20

Give some characteristics of low-level languages.

Answer 20

1) one instruction of assembly code usually only represents one instruction of machine code
2) usually written for one type of machine or processor and won’t work on any others
3) the programmer needs to know about the internal structure of the CPU and how it manages the memory
4) code is very difficult to read, understand and modify
5) commands in machine code can be executed directly without the need for a translator
6) you control exactly what the CPU does and how it uses memory so programs will be more memory efficient and faster

Question 21

What are the three types of translators?

Answer 21

1) assemblers
2) compilers
3) interpreters

Question 22

What are assemblers used for?

Answer 22

To turn assembly language into machine code

Question 23

What are compilers and interpreters used for?

Answer 23

To turn high-level code into machine code

Question 24

Give some characteristics of compilers.

Answer 24

1) translates all of the source code at the same time and creates one executable file
2) only needed once to create the executable file
3) returns a list of errors for the entire program once compiling is complete
4) once compiled the program runs quickly, but compiling can take a long time

Question 25

Give some characteristics of interpreters.

Answer 25

1) translates and runs the source code one instruction at a time, but doesn’t create an executable file
2) needed every time you want to run the program
3) the interpreter will return the first error it finds and then stop - this is useful for debugging
4) programs will run more slowly because the code is being translated as the program is running