Topic 1.8 - Program Construction

Question 1

What is the function of translation programs?

Answer 1

The translation program converts the high level source code into low level assembly language (or machine code) ready for execution.

Question 2

What is the purpose of an assembler?

Answer 2

An assembler converts code written in assembly language into object code (machine code or binary) ready for execution by the computer.

Question 3

What is the difference between a compiler and an interpreter?

Answer 3

A compiler compiles all the code in one go by converting it from high level language to a file object code before executing. (Use for publishing and all-round)
An interpreter converts each line of code into machine code one at a time before executing it. After one line has been converted, the next line can be translated. (Usually used for debugging and testing)

Question 4

What are the 4 stages of compilation?

Answer 4

• Lexical Analysis
• Syntax Analysis
• Semantic Analysis
• Code Generation

Question 5

What happens during lexical analysis?

Answer 5

• Input stream broken into tokens
• Comments removed
• Necessary spaces are removed
• Error messages created if appropriate

Question 6

What happens during syntax analysis?

Answer 6

• A symbol table/dictionary is created
• Tokens are checked against grammar rules (BNF)
• If tokens are invalid, error messages are produced

Question 7

What happens during semantic analysis?

Answer 7

• Checks all variables are declared and used
• Checks that data of the appropriate data types are assigned to values declared as such data types
• Error messages produced if necessary
• Checks that all operations are legal (reverse polish notation is used)

Question 8

What happens during code generation?

Answer 8

• Machine code is generated

- Code optimisation may take place

Question 9

What is a subprogram library?

Answer 9

This is a library which contains subprograms and subroutines. The main program can then call these subroutines from the library by importing (linking) the library.

Question 10

What is a link loader?

Answer 10

This is a piece of software which can load parts of programs stored in different locations and link them together.

Question 11

Name and describe two translation errors

Answer 11

Syntax error - Where code has been written outside the grammar of the language
Run-time error - e.g Trying to divide by 0 when the program is running