Question

5-Write an EBNF rules that describes the following while statement of Java. Then, write the recursive-descent subprogram in Java or C/C++ for the EBNF rule. Please summit your source code and a screen shot of the parsing of the following examples.

do { if ( number % 2 == 0 ) even ++; number=number+1; } while (number <= 10)

Answer 1

EBNF rules for while statement :

<while_stmt> -> WHILE ‘(‘ ( <arith_expr> | <logic_expr> ) ‘)’

<block> <block> -> <stmt> | ‘{‘ <stmt> {<stmt>} ‘}’

Source Code of the parsing of the given example :

import java.util.*;

public class ParseString

{

          public static void main(String args[])

          {

                       StringTokenizer st1 = new StringTokenizer("do { if ( number % 2 == 0 ) even ++ ; number = number + 1 ; } while ( number <= 10 ) ", " ");    // StringTokenizer Class allows string to break into tokens.

                       int count=0;

                       while (st1.hasMoreTokens())   // It test if more tokens are available or not.

                       {

                                count++;

                                System.out.println("Token "+count+" "+st1.nextToken()); //Returns next token in the string.

                        }

                       System.out.println("Total Tokens :: "+count);

          }

}

Output (Snapshot) :