Question

Exercises: Home Work to do :

  

1)   write BNF grammars for the following sententials: lexemes (not tokens)

-  positive and negative integer numbers

-  floating point numbers

-  variable names in C

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2)   check (recognize) if this code can derive from the given grammar ?



-  swith (tatal)

        {

        case total > 1000 :  cout<<"expensive"; break;

        case total = 1000 :  cout<<"exact";     break;

        case total < 1000 :  cout<<"cheap";     break;

        }

Answer 1

1.

BNF Grammar for

a. positive and negative integer numbers

<number> ::= <num> | - <num>

<num> ::= <digit> | <num> <digit>

<digit> ::= 0|1|2|3|4|5|6|7|8|9

Here, a number can be simply a number or it can be a negative number(preceded by -)

Num can be a digit or a num followed by digit

A digit can be 0 or 1 or 2.... or 9

b. Floating point numbers

<real> ::= <num>.<fraction>

<num> ::= <digit> | <num> <digit>

<fraction> ::= <digit> | <digit> <fraction>

<digit> ::= 0|1|2|3|4|5|6|7|8|9

A floating point number can a num followed by . (dot) followed by fractional part

Num can be a digit or a num followed by digit

A digit can be 0 or 1 or 2.... or 9

A fractional part can a digit or a digit followed by a fraction

c. Variable names in C

<var> ::= <letter> | <letter> <word>

<word> ::= <letter> | <digit> | <letter><word> | <digit><word>

<letter> ::= a |b|c|.....|y|z|_

<digit> ::= 0|1|2|3|4|5|6|7|8|9

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