CS 401/501 EXAM #1 SAMPLE QUESTIONS
1. Explain the difference between a token and a lexeme. (5%)
2. For each regular expression below provide a brief description what kind of lexemes
are going to match with a pattern and provide some examples of lexemes (at least 3).
[pr]?ink
[a-z][a-z0-9]*
[1-9][0-9][0-9]
/\*[^\*]+\*/
([a-c][0-9])+ (10%)
3. Write a BNF grammar for a language, in which programs always start with the
keyword “print” followed by arithmetic expression (+ or -). The later is optionally followed
by a declaration part, starting with the keyword “where” and a list of pairs “id=num”
which are separated with “,”. Few examples:
print 10
print a+10 where a=1
print a+b-c where a=2, b=4, c=21 (20%)
4. Perform left factoring on the production
B ::= spring A | spring num C (5%)
5. Write a recursive descent parser for the following LL(1) grammar. Assume the
existence of a scanning procedure GET_TOKEN which sets a global string variable
TOKEN to the token type of the next token.
P ::= D begin S end
D ::= var V
V::= T V | ε
T ::= int id ; | real id ;
S ::= id := num S | ε
Draw a parse tree for the sentence: var int i; int j; begin end (25+5%)
6. Write an attribute grammar for a following grammar:
Eq ::= Sum = Sum
Sum ::= Prod AddOp Sum | Prod
Prod ::= Fact MulOp Prod | Fact
Fact ::= ( Sum ) | num
AddOp ::= + | -
MulOp ::= * | /
