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Msword CD

The document contains yacc/lex code to recognize and evaluate valid arithmetic expressions using the operators +, -, *, and /. The lexer identifies numbers and operators, while the parser evaluates the expressions with proper operator precedence, handling errors such as division by zero. The program prompts the user for input and outputs the result of the evaluated expression.

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4 views7 pages

Msword CD

The document contains yacc/lex code to recognize and evaluate valid arithmetic expressions using the operators +, -, *, and /. The lexer identifies numbers and operators, while the parser evaluates the expressions with proper operator precedence, handling errors such as division by zero. The program prompts the user for input and outputs the result of the evaluated expression.

Uploaded by

ayushdwdi63
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Q22.

Design a yacc/lex code to recognize valid arithmetic expression with operators +,-,*
and /.

Program

(prog.l):

%{
#include "y.tab.h"

%}

%%

[0-9]+ { yylval = atoi(yytext); return NUMBER; }


"+" { return PLUS; }

"-" { return MINUS; }

"*" { return MUL; }

"/" { return DIV; }

[ \t] {}

. { printf("Unexpected character: %s\nINVALID expression", yytext); exit(1); }

%%

int yywrap(){
return 1;
}

(prog.y)

%{

#include <stdio.h>

Ayush Dwivedi Sec- A1 Roll No. 15


#include <stdlib.h>

%}

%token NUMBER

%token PLUS MINUS MUL DIV

%%

expr:

expr PLUS expr

| expr MINUS expr

| expr MUL expr

| expr DIV expr


| NUMBER

%%

int yyerror(const char *s){

fprintf(stderr, "Error: %s\n", s);

exit(1);
}

int main(){

printf("Enter an arithmetic expression: ");

if(yyparse() == 0){
printf("This is a valid expression\n");

else printf("This expression is invalid\n");


return 0;
}

Ayush Dwivedi Sec- A1 Roll No. 15


OUTPUT:

Ayush Dwivedi Sec- A1 Roll No. 15


Q23. Design a yacc/lex code to evaluate arithmetic expression with operators +, -, *, and
/ with operator precedence.

Program
(prog.l):

%{
#include "y.tab.h"

%}

%%

[0-9]+ { yylval = atoi(yytext); return NUMBER; }


[+\-*/] { return yytext[0]; }
"\n" { return '\n'; }

[ \t] { /* Ignore whitespace */ }

. { printf("Unexpected character: %s\nINVALID expression\n", yytext); exit(1); }

%%
int yywrap(){

return 1;
}

(prog.y):

%{

#include <stdio.h>

#include <stdlib.h>
%}

Ayush Dwivedi Sec- A1 Roll No. 15


%token NUMBER

%left '+' '-'

%left '*' '/'

%%

stmt:

expr '\n' { printf("The result is: %d\n", $1); }

;
expr:

expr '+' expr { $$ = $1 + $3; }


| expr '-' expr { $$ = $1 - $3; }

| expr '*' expr { $$ = $1 * $3; }

| expr '/' expr {


if($3 == 0){

fprintf(stderr, "Cannot divide by 0\n");

exit(1);
}

else{

$$ = $1 / $3;

| NUMBER { $$ = $1; }

;
%%

int yyerror(const char *s){

fprintf(stderr, "Error: %s\n", s);

exit(1);

Ayush Dwivedi Sec- A1 Roll No. 15


}

int main(){

printf("Enter an arithmetic expression:\n");

yyparse();
return 0;
}

Output

Ayush Dwivedi Sec- A1 Roll No. 15


Ayush Dwivedi Sec- A1 Roll No. 15

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