NATIONAL OPEN UNIVERSITY OF NIGERIA

UNIVERSITY VILLAGE, PLOT 91, CASDASTRAL ZONE, NNAMDI AZIKIWE EXPRESS WAY, JABI, ABUJA.
FACULTY OF SCIENCES
OCTOBER 2019 EXAMINATION

COURSE CODE: CIT445
COURSE TITLE: PRINCIPLES AND TECHNIQUES OF COMPILERS
CREDIT: 3 UNITS
TIME ALLOWED: 2½ HOURS
INSTRUCTION: ANSWER QUESTION 1 AND ANY OTHER FOUR (4) QUESTIONS

1a) Explain what is meant by top-down parsing technique (2 marks)
b) State the difficulties in top-down parsing (6 marks)
c) Analyse the errors which can be detected during lexical analysis. (6 marks)
d) What is meant by the "front end" of a compiler? (2 marks)
e) List the phases that constitute the front end of a compiler. (4 marks)
f) State two (2) of the uses of formal languages (2 mark)

2a) ) With the aid of a suitable diagram, clearly state the use of T-diagrams (4 marks)
b) Discuss any five (5) qualities of compilers (5 marks)
c) How are the following represented?
i) Grammar symbols (1 mark)
ii) strings of terminals (1 mark)
iii) productions (1 mark)

3a) ) List the steps to implement Lex. (5 marks)
b) Explain the process of creating a lexical processor with Lex (4 marks)
c) Identify any three (3) roles of the Parser (3 marks)

4a) State the constituents of a Context-Free Grammar (CFG) (4 marks)
b) State the usefulness of CFGs. (2 marks)
c) Write short notes on the following:
(i) Operator precedence parser (2 marks)
(ii) operator Grammar (2 marks)
(iii) operator precedence e Grammar (2 marks)

5a) Express the operator precedence parser algorithm. (9 marks)
b) Briefly describe a “parser”. (3 marks)
6a) Suppose we have a grammar G:
E → E + T
E → T
T → T*F
T → F
F → (E)
F → a
i) Find the left parse of the sentence a *(a + a) stating the production rule applied at each stage. (8¼ mark)
ii) State the sequence of derivation. (¼ mark)
b) Write short notes on Bottom-up Parsing. (3½ marks)