JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III COMPILER DESIGN Previous Question Paper (March - 2021 - R13/R15)

The following LEX program identifies specific C reserved words such as if, else, while, and for:

%{ #include <stdio.h> %}
%%
if|else|while|for { printf("%s is a reserved word\n", yytext); }
[a-zA-Z_][a-zA-Z0-9_]* { printf("%s is an identifier\n", yytext); }
.|
 { ; }
%%
int yywrap() { return 1; }
int main() { yylex(); return 0; }

A grammar is ambiguous if there exists at least one string in its language that has more than one leftmost derivation, more than one rightmost derivation, or more than one parse tree. Ambiguity often arises in expressions where operator precedence or associativity is not defined.

Left recursion occurs when a non-terminal A can derive a string starting with itself, typically in the form

Where A' is a new non-terminal and ε represents the empty string. If the grammar is ambiguous, it must first be rewritten to enforce precedence and associativity rules (e.g., by introducing new non-terminals for terms and factors) before applying the left recursion elimination algorithm.