The Function and Purpose of Translators

Question 1

Define assembly language.

Answer 1

A low level language that uses mnemonics and labels to represent a full set of instructions.

Question 2

What is the assembler?

Answer 2

A piece of software that translates assembly language into machine code.
The assembler must be machine specific.

Question 3

Define high level language.

Answer 3

A high level language written as source code. It is understandable by the programmer often using keywords to represent instructions.

Question 4

Define machine code.

Answer 4

• binary notation/executable form
• set of all instructions available
• (instructions operate on) bytes of data
• dependent on architecture/processor design

Question 5

What is an interpreter?

Answer 5

A translator program that translates source code one line at a time into machine code.

Question 6

What is an interpreter useful for and why?

Answer 6

Debugging and testing as it returns accurate error messages as they arrive.

Question 7

What is a compiler?

Answer 7

A translator program that translates the source code as a unit into machine code to produce an executable program file.

Question 8

What is the purpose of intermediate code?

Answer 8

• It can run on a variety of machines using an interpreter
• Improves portability
• Allows sections of programs to be written in different languages
• Used in a virtual machine

Question 9

What additional software is needed to run the intermediate code?

Answer 9

An interpreter/ Virtual Machine

Question 10

What is the main purpose of a translator?

Answer 10

• To translate source code into object code

- To detect and report any errors

Question 11

What are the disadvantages of using intermediate code?

Answer 11

• program runs more slowly
• has to be translated each time program is run
• needs additional software

Question 12

What does optimisation do?

Answer 12

• make code as efficient as possible
• increases processing speed
• reduces the number of instructions

Question 13

What are the features of an interpreter?

Answer 13

• translates one line at a time
• runs each line before translation of next
• reports one error at a time and then stops
• indicates the position of the error

Question 14

What are the disadvantages of using an interpreter?

Answer 14

• Program runs more slowly due to translation each time

- Additional software is needed every time the program is run

Question 15

What are the advantages of using a compiler?

Answer 15

• Protects programs from malicious use
• Optimisation improves program speed
• Compiler is no longer needed once executable file is produced.

Question 16

Describe the steps an assembler performs when producing machine code.

Answer 16

• reserves storage for instructions & data
• replaces mnemonic opcodes by machine codes
• replaces symbolic addresses by numeric addresses
• creates symbol table…
• …to match labels & addresses
• checks syntax/gives error diagnostics

Question 17

Why are library routines used?

Answer 17

• to perform common tasks
• they are error-free/have been tested
• ready to use/saves work/saves time
• may be used multiple times
• may have been written in different source language
• use other programmers’ expertise

Question 18

What are the stages of compilation?

Answer 18

• syntax analysis
• lexical analysis
• code generation

Question 19

What happens during syntax analysis?

Answer 19

• accepts output from lexical analysis
• statements/arithmetic expressions/tokens are checked…
• …against the rules of the language/valid example given eg matching brackets
• errors are reported as a list (at the end of compilation)
• diagnostics may be given
• (if no errors) code is passed to code generation
• further detail is added to the symbol table…
• …eg data type /scope/address

Question 20

Explain the term intermediate code and its use.

Answer 20

• simplified code / partly translated code…
• …which can be run on any computer/virtual machine/improves portability…
• …using an interpreter
• sections of program can be written in different languages
• runs more slowly than executable code

Question 21

What software is used to convert source code into object code?

Answer 21

translator

Question 22

Explain the term source code.

Answer 22

• the original code/code written by the programmer…
• …often in a high level language
• may be in assembly language
• source code can be understood by people…
• …but cannot be executed (until translated)

Question 23

What is a library routine?

Answer 23

• routines are pieces of software…
• …which perform common tasks…
• …such as sorting/searching
• routines are compiled

Question 24

How are library routines used?

Answer 24

• linker is used…
• …to link routine with program
• loader handles addresses…
• …when program is to be run

Question 25

Describe code generation.

Answer 25

• Occurs after syntax analysis/is last phase of
  compilation
• Produces machine code program/executable
  code/intermediate code…
• …which is equivalent to the source program
• Variables/constants are given addresses
• Relative addresses are calculated.

Question 26

Describe optimisation.

Answer 26

• Makes code as efficient as possible
• Increases processing speed
• Number of instructions is reduced