Translators Exam Questions

• B Compiler (1)
• The only correct answer is B. The correct answer is compiler.
• A is not correct because an assembler translates assembly language code into machine code, not a high-level program
• C is not correct because an interpreter translates and executes the code line by line, without producing a complete machine code program first
• D is not correct because a linker combines object code files into a single executable, it does not translate source code

• A Executes the line (1)
• The only correct answer is A. The correct answer is that the interpreter executes the line.
• B is not correct because an interpreter does not produce object code; that is what a compiler does
• C is not correct because an interpreter does not save the translated code to a file
• D is not correct because the interpreter executes the current line before it translates the next line

• B At the end of translating the program (1)
• The only correct answer is B. The correct answer is at the end of translating the program.
• A is not correct because a compiler translates the whole program and does not report an error after each line; reporting after each line is how an interpreter behaves
• C is not correct because a compiler does not stop at the first error; it finishes translating and reports the errors it finds at the end
• D is not correct because syntax errors are found during translation, before the object code is run

• C The object code is saved as a separate file (1)
• The only correct answer is C. The correct answer is the object code is saved as a separate file.
• A is not correct because a compiled program is not translated again when it is run
• B is not correct because translating one line at a time is how an interpreter works
• D is not correct because the source code is not needed to run a compiled program

Award one mark for:

• The whole program (before it is run) (1)

Allow all of the code/the entire program/the whole program in one go

Do not accept one line/statement at a time or each line as it is executed

Do not accept translating only the lines that contain errors

Award one mark for any of the following:

• Object code (1)
• Machine code (1)
• Executable code / an executable (1)

Allow object file.

Do not accept source code.

Do not accept high-level code.

Award one mark for any of the following:

• Translation/execution stops (when the error is found) / the rest of the program is not translated/executed (1)

Allow stops/terminates/halts when the error is found

Do not accept shows/displays an error message on its own

Do not accept the whole program is translated and errors are reported at the end

Do not accept translates line by line on its own

Award one mark for any of the following up to a maximum of two marks:

• Translates/converts (high-level/source) code one line/statement at a time (1)
• Translates/converts the code and executes/runs each line as it goes (1)
• Executes/runs each line/statement immediately after it is translated (1)
• Reports/stops with an error message as soon as a syntax error is found (1)

Allow 'runs' for executes, 'converts' for translates and 'instruction' for line/statement

Do not accept translates the whole program before it is run

Do not accept produces/creates object code, an executable file or machine code that is saved

Award up to two marks for a linked description such as:

• The compiler translates the whole program/complete source code in one go (1) whereas the interpreter translates one line/statement at a time (1)
• The compiler translates all of the source code before any of it is run/executed (1) but the interpreter translates each line/statement as it reads it (1)
• The interpreter translates one line/statement at a time (1) and the compiler translates the whole program/source code together (1)

Accept the compiler point and the interpreter point in either order.

Do not accept responses about object code/executable files, when the translated code is executed, how errors are reported, or speed/memory use.

Do not accept 'the interpreter executes/runs each line' on its own, without saying that it translates one line/statement at a time.

Award up to two marks for a linked description such as:

• A compiler produces object code/machine code/an executable (file) (1) whereas an interpreter produces no object code/translated file (1)
• A compiler produces a machine code file (1) that can be run on its own/without the compiler/translator being present (1)
• An interpreter produces no object code/file (1) because it translates and executes each line instead of saving translated code (1)
• The compiler's output can be saved/stored (1) and run again later, while interpreted code has to be translated again each time it is run (1)

Allow binary for machine code.

Allow executable/an executable for object code.

Do not accept responses about translating the whole program, reporting errors or the speed of execution.

Do not accept 'the interpreter translates/executes one line at a time' on its own: this is how it translates, not what it produces. It earns the development only when linked to no object code/translated file being produced.

Do not accept the interpreter producing object code/an executable.

Award up to two marks for a linked description such as:

• The interpreter executes each line as soon as it has been translated (1) so translation and execution happen together/at the same time (1)
• The compiler translates the whole program first (1) and the machine code is run later/separately (1)
• The interpreter translates the code and runs it while the program is running (1) whereas the compiler does not run the code it produces (1)
• The compiler produces translated code that is executed only after all the translation has finished (1) but the interpreter executes each line immediately (1)

Allow 'translates one line at a time' where it is linked to executing each line immediately.

Do not accept answers that only state that a compiler is faster/an interpreter is slower, without reference to when execution happens.

Do not accept answers that only give object code, error reporting or portability, without reference to when execution happens.

Do not accept the compiler executing the program as it translates it.

Award up to two marks for a linked description such as:

• The compiler reports all syntax errors after translation has finished (1) whereas the interpreter stops at the first error it finds (1)
• The interpreter reports a syntax error as soon as it finds one (1) and does not translate/execute any more of the program (1)
• The compiler continues translating after an error (1) and reports the errors at the end (1)
• The interpreter stops translating when it reaches an error (1) but the compiler finishes translating before reporting errors (1)

Do not accept answers about fixing/correcting errors or about object code.

Do not award 'the compiler finds more errors' without saying errors are reported at the end.

Award up to two marks for a linked explanation such as:

• The compiler produces object code/machine code for the whole program (1) so there is no complete executable until every line has been translated (1)
• The compiler translates all the source code before producing the object code (1) so the program cannot start until translation has finished (1)
• The compiler checks the whole program for errors during translation (1) so all of the source code must be read before an executable can be produced (1)

For both marks, the expansion must follow/associate with the statement.

Allow 'in one go'/'all at once' for the translation point, but this does not earn the second mark unless it is linked to why the program cannot be executed until translation has finished.

A statement that the whole program is translated, with no linked reason about when the program can be executed, earns 1 mark only.

Do not accept 'a compiler is faster' or 'compiled code runs faster' on its own; this does not explain why translation must finish before execution.

Do not accept 'it translates and runs the program one line at a time', as this describes an interpreter.

Award up to two marks for a linked explanation such as:

• No object code/machine code file is stored/saved (1) so there is no translated program to run on the next occasion (1)
• The translation is only temporary/is lost when the program ends (1) because each line is translated as the program runs (1)
• No executable file is created/saved (1) so the whole program has to be translated again every time it is run (1)
• The interpreter translates each line while the program is running (1) so nothing is kept that could be run without the interpreter (1)

For both marks, the expansion must follow/associate with the statement.

Do not accept 'it is interpreted' or 'it is not compiled' without saying that no object code/executable is stored/saved.

Do not accept 'the source code is high-level so it must be translated' or 'the source code has to be turned into machine code' on its own, as this is true of any translation.

Do not accept answers about the source code being deleted.

Award up to two marks for a linked explanation such as:

• The interpreter translates and executes each line in turn (1) so it cannot continue past a line it cannot translate (1)
• The interpreter finds the error when it reaches that line (1) so it stops and displays an error message before later lines are executed (1)
• Each line is translated just before it is executed (1) so a syntax error in that line prevents that translation/execution from happening (1)
• The interpreter does not translate the whole program first (1) so it only discovers the error when that line is reached during execution (1)

For both marks, the expansion must follow/associate with the statement.

Do not accept 'the program crashes' without saying that the interpreter cannot translate/execute the line.

Do not accept answers about how a compiler reports errors.

Award up to two marks for a linked explanation such as:

• The compiler translates the whole program into machine code before it is run (1) so no translation is needed while the program is executing (1)
• The machine code/object code is already produced before execution (1) so the CPU can carry out the instructions directly without translating them (1)
• The compiled program does not need an interpreter at run time (1) so no time is spent translating each line before it is executed (1)

For both marks, the expansion must follow/associate with the statement.

A statement that translation happens before execution, with no linked reason for faster running, earns 1 mark only.

Do not accept 'faster to run' or 'quicker' on its own without a reason linked to translation before/during execution.

Do not accept 'compiled code is optimised' or 'compilation takes less time' without linking this to translation before execution/at run time.

Do not accept answers about the compiler being installed or available.

The question asks why a compiled program usually runs faster, so answers must refer to when translation happens, not just general performance claims.

Indicative content

The output of each type of translator

• A compiler translates the whole program in one go and produces object code.
• The object code is saved as an executable file, which is already in machine code so the processor can run it directly.
• An interpreter does not produce object code, so no translated file exists for the company to save and sell.
• An interpreter translates one line at a time and executes it immediately, but that translation is not kept.

Whether the program has to be translated each time it is run

• Compiled code is translated once, so the executable can be run as many times as the customer likes without being translated again.
• If the source code is edited, the whole program has to be compiled again to produce a new executable.
• An interpreted program is translated again every time it is run, so a customer who runs the program often waits for translation at every run.
• An executable runs faster than interpreted code because it is already in machine code.

What the customer needs on their computer to run the program

• A customer who installs the executable needs no compiler on their computer, so the program will run straight away.
• If the company supplied the source code instead, the customer would need an interpreter installed, and it would have to be an interpreter for their type of computer.
• A customer given only the executable does not have the source code, so cannot change the program.

Conclusion

• A compiler is the better choice for this company, because the executable can be sold and the customer runs it without it being translated again and without being given the source code.
• Using an interpreter would mean supplying the source code to customers and translating the program on every run.

Levels

• Level 0 (0 marks): No rewardable content.
• Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
• Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
• Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Level 3 responses must cover all three bullets for this company's program, including translating once rather than on every run, and reach a conclusion.

Do not accept 'a compiler fixes errors' (a compiler reports syntax errors at the end of translation, it does not fix them) or 'a compiler is easier to use' with no link to output, translation or the customer. Do not accept answers about translating to assembly language.

Indicative content

How each translator deals with a syntax error

• An interpreter stops as soon as it finds a syntax error and displays an error message.
• With an interpreter, the lines before the error have already been executed, so the student can see how far the program got before it stopped.
• A compiler reports errors at the end of translation, so the student gets a list of all the syntax errors in the program in one go.

How much of the program is translated at a time

• An interpreter translates one line at a time and executes each line immediately.
• A compiler translates the whole program in one go before any of it is run.
• A compiler produces object code, so after every change the whole program must be compiled again before the student can run it.
• An interpreter produces no object code, so the student does not have to wait for the whole program to be translated before it runs.

How this affects the student's testing

• An interpreter suits this student because the program can be run straight away after each small change.
• The interpreter stops at the first error found, so the student fixes that error and runs the program again, but may only find the next error on the next run.
• Reporting every error at the end of compilation means the student can fix several errors at once, but cannot run the program until the whole program compiles.
• The student should use an interpreter while testing, and compile the finished program once it works.

Levels

• Level 0 (0 marks): No rewardable content.
• Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
• Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
• Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Level 3 responses must relate the way each translator works to the student's testing, not just describe the two translators.

Do not accept answers about run-time or logic errors where no comparison of the translators is made.