===== Page 6 =====


Q1. Design a LEX Code to count the number of lines, space, tab-meta character, and rest of characters in each Input pattern.


Solution:

% {

#include<stdio.h>

int line = 0 , space = 0 , tab = 0 , meta = 0 , other = 0;

% }


%%

"\n"    {line++;}

" "    {space++;}

"\t"    {tab++;}

[\^\$\%\*\+\^\&\()\{}\}[]\v\"] {meta++;}

.    {other++;}

%%


int main(){

    yylex();

    printf("Line:%d\n",line);

    printf("Space:%d\n",space);

    printf("Tab:%d\n",tab);

    printf("Meta:%d\n",meta);

    printf("Other:%d\n",other);


    return 0;

}


int yywrap(){

    return 1;

}


Output:


int main(){

    cout << "hello";

}

Line:3

Space:3

Tab:1

Meta:7

Other:18


===== Page 7 =====


Q2. Design a LEX Code to identify and print valid Identifier of C/C++ in given Input pattern.


Solution:


% {

    #include<stdio.h>

% }


%%

int|float|return|void|if|else    { }

[a-zA-Z_]+[a-zA-Z_0-9]*    { printf("Identifier:%s\n",yytext);}

[0-9]+[a-zA-Z_]*

.    { }

%%


int main(){

    yylex();

    return 0;

}


int yywrap(){

    return 1;

}


Output:

var_43

Identifier:var_43


num

Identifier:num


temp

Identifier:temp


6


===== Page 8 =====


Q3. Design a LEX Code to identify and print integer and float value in given Input pattern.


Solution:


% {

    #include<stdio.h>

% }


%%

[-]?[0-9]+"."[0-9]+    {printf("Float:%s\n",yytext);}

[-]?[0-9]+    {printf("Int:%s\n",yytext);}

[0-9]*[a-zA-z]*[0-9]*    {printf("Nothing");}

.    {}


%%


int main(){

    yylex();

    return 0;

}


int yywrap(){

    return 1;

}


Output:

1234

Int:1234


123.54

Float:123.54


45_frr

Nothing


===== Page 9 =====


Q4. Design a LEX Code for Tokenizing (Identify and print OPERATORS, SEPERATORS, KEYWORDS, IDENTIFERS) in the C-fragment:


Solution:


% {

    #include<stdio.h>

}


% }


KEYWORDS "int"|"float"|"return"|"if"|"else"|"for"|"while"

OPERATORS [+|\-|*|/|^|<|>|&|!|%]

SEPERATORS [;|\\|(|)|\\|\\|']


%%

{ KEYWORDS } {printf("Keyword: %s\n", yytext); }

{ OPERATORS } {printf("Operators: %s\n", yytext); }

{ SEPERATORS } {printf("Seperators: %s\n", yytext); }

[a-zA-Z_]+[a-zA-Z0-9_]* {printf("Id: %s\n", yytext); }

. {}

%%


int main(){

    yylex();

    return 0;

}


int yywrap(){

    return 1;

}

                                                   OR 

%{

#include <stdio.h>

%}


%option noyywrap


KEYWORDS    "int"|"float"|"return"|"if"|"else"|"for"|"while"

OPERATORS   [+\-*/^<>=&|!%]=?|&&|\|\||==|!=

SEPARATORS  [;,(){}"\[\]]

IDENTIFIER  [a-zA-Z_][a-zA-Z0-9_]*


%%


{KEYWORDS}     { printf("Keyword: %s\n", yytext); }

{OPERATORS}    { printf("Operator: %s\n", yytext); }

{SEPARATORS}   { printf("Separator: %s\n", yytext); }

{IDENTIFIER}   { printf("Identifier: %s\n", yytext); }

[ \t\n]        ;  // Ignore whitespace

.              ;  // Ignore any other character


%%


int main() {

    yylex();

    return 0;

}

Output:

int

Keyword: int


+

Operators: +


;


Seperators: ;


var_23

Id: var_23


===== Page 10 =====


Q5. Design a LEX Code to count and print the number of total characters, words, white spaces in given ‘Input.txt’ file.


Solution:


% {

    #include<stdio.h>

    int word =0, char_len=0, space = 0;

% }


%%

[a-zA-Z0-9]+ {

    word++;

    char_len += yyleng;}

[ \n\t] {space++;}


%%


int main(){

    FILE *file = fopen("z-5-6.txt", "r");

    if(!file) {printf("no file"); return 1;}

    }

    yyin = file;

    yylex();

    printf("word:%d\n",word);

    printf("char:%d\n",char_len);

    printf("space:%d\n",space);

    fclose(file);

    return 0;

}


int yywrap() {

    return 1;

}


Output:

word:7

char:46

space:48


===== Page 11 =====


Q6. Design a LEX Code to replace white spaces of ‘Input.txt’ file by a single blank character into ‘Output.txt’ file


Solution:


% {

#include <stdio.h>

#include <stdlib.h>

FILE *out;

% }


%%

[ \n\t]+ { fprintf(out, " ");

    // Replace multiple spaces, tabs, or newlines with a single space

    }

.    { fprintf(out, "%s", yytext); } // Write other characters as they are

%%


int main() {

    // Open input and output files

    yyin = fopen("z-5-6.txt", "r");

    if (!yyin) {

    perror("Error opening input.txt");

    return 1;

}


out = fopen("output.txt", "w");

if (!out) {

    perror("Error creating output.txt");

    fclose(yyin);

    return 1;

}

yylex();


fclose(yyin);

fclose(out);


printf("Whitespace replaced successfully. Check output.txt\n");

return 0;

}


int yywrap(){

    return 1;

}


Output:

input : hello my name is justin

jhdfhejdjjdejdjehd ehidhehdhd


output :

hello my name is justin jhdfhejdjjdejdjehd ehidhehdhd


10


===== Page 12 =====


Q7. Design a LEX Code to remove the comments from any C-Program given at run-time and store into ‘out.c’ file.


Solution:

% {

#include <stdio.h>

#include <stdlib.h>

FILE *out;

% }


%%

"//".*    { }

"/\\*([^*]|\\*+[^*/])*\\*+\\/" { }

.    { fprintf(out, "%s", yytext); }

\n    { fprintf(out, "\n"); }


int main() {

    char input_file[100];


    printf("Enter the C program filename (e.g., program.c): ");

    scanf("%s", input_file);


    yyin = fopen(input_file, "r");

    if (!yyin) {

    perror("Error opening input file");

    return 1;

    }


    out = fopen("out.c", "w");

    if (!out) {

    perror("Error opening out.c");

    fclose(yyin);

    return 1;

    }

    yylex();


    fclose(yyin);

    fclose(out);


    printf("Comments removed successfully. Check out.c\n");

    return 0;

}


int yywrap(){

    return 1;

}


Output:

input :

#include <stdio.h> // header file


===== Page 13 =====


int main()

{

    // program start

    printf("Hello"); // print strnt

}

// exit


output :

#include <stdio.h>

int main()

{

    printf("Hello");

}


12


===== Page 14 =====


Q8. Design a LEX Code to extract all html tags in the given HTML file at run time and store into Text file given at run time.


Solution:

% {

#include <stdio.h>

#include <stdlib.h>

FILE *out;

% }

%%

\<!--([^-|n]|(-[^-])|(|n))*--> { }

\<[a-zA-Z/1][^>]*> { fprintf(out, "%s\n", yytext); }

.    { }

\n    { fprintf(out, "\n"); }

%% 

int main() {

    char input_file[100], output_file[100];


    printf("Enter the HTML file name (e.g., index.html): ");

    scanf("%s", input_file);


    printf("Enter the output file name (e.g., tags.txt): ");

    scanf("%s", output_file);


    yyin = fopen(input_file, "r");

    if (!yyin) {

    perror("Error opening input file");

    return 1;

}


    out = fopen(output_file, "w");

    if (!out) {

    perror("Error opening output file");

    fclose(yyin);

    return 1;

}

yylex();

fclose(yyin);

fclose(out);

printf("HTML tags extracted successfully. Check %s\n", output_file);

return 0;

}

int yywrap(){

    return 1;

}


===== Page 15 =====


Q9. Design a DFA in LEX Code which accepts string containing even number of ‘a’ and even number of ‘b’ over input alphabet (a, b).


Solution:

% {

#include <stdio.h>

#include <ctype.h>


int state = 0;

int invalid_input = 0;

% }


%% 

a { 

    if (state == 0) state = 1; 

    else if (state == 1) state = 0; 

    else if (state == 2) state = 3; 

    else if (state == 3) state = 2; 

}


b { 

    if (state == 0) state = 2; 

    else if (state == 1) state = 3; 

    else if (state == 2) state = 0; 

    else if (state == 3) state = 1; 

}


[c-zC-Z0-9]+ { 

    invalid_input = 1; 

}


\n { 

    if (invalid_input == 1) { 

    printf("Rejected (Invalid characters found)\n"); 

} else if (state == 0) { 

    printf("Accepted\n"); 

} else { 

    printf("Rejected\n"); 

} 

state = 0; 

invalid_input = 0; 

}


. { /* Ignore spaces or special characters */ }

%% 


int main() { 

    char input[100]; 

while (1) {


===== Page 16 =====


printf("Enter a string of a's and b's (end with Enter, type 'exit' to quit): ");

fgets(input, sizeof(input), stdin);

if (input[0] == 'e' && input[1] == 'x' && input[2] == 'i' && input[3] == 't') {

    break;

    }

    yylex();

}


return 0;


}


int yywrap(){

    return 1;

}


Output:


Enter a string of a's and b's (end with Enter, type 'exit' to quit):

aabb

Accepted

abab

Accepted

bbaab

Rejected


15


===== Page 17 =====


Q10. Design a DFA in LEX Code which accepts string containing third last element ‘a’ over input alphabet (a, b).


Solution:

% {

#include <stdio.h>

#include <string.h>

char window[4] = "   "; 

% }

%%

[a|b] {

    window[0] = window[1];

    window[1] = window[2];

    window[2] = yytext[0];

}

\n {

    if (strlen(window) >= 3 && window[0] == 'a') {

    printf("Accepted\n");

    } else {

    printf("Rejected\n");

    }

    strcpy(window, "   ");

    }

.    { }

%%

int main() {

    char input[100];

    while (1) {

    printf("Enter a string of a's and b's (end with Enter, type 'exit' to quit): ");

    fgets(input, sizeof(input), stdin);

    if (strncmp(input, "exit", 4) == 0) {

    break;

    }

    yylex();

    }

    return 0;

    }

    int yywrap(){

    return 1;

    }

}


Output:

aabb

Accepted

aaabbb

Rejected

aaaaab

Accepted


===== Page 18 =====


Q11. Design a DFA in LEX Code to Identify and print Integer &amp; Float Constants and Identifier.


Solution:

% {

#include <stdio.h>

% }


%%

([0-9]+)    {printf("Integer: %s\n", yytext);}


([0-9]+\.[0-9]+) | (\.[0-9]+) | ([0-9]+\.) {printf("Float: %s\n", yytext); }


[a-zA-Z_]+[a-zA-Z_0-9]*    {printf("Identifier: %s\n", yytext); }


[\n\t ]+    { }


.    {printf("Unrecognized token: %s\n", yytext);}

%%


int main() {

    printf("Enter your input (type 'exit' to quit):\n");

    yylex();

    return 0;

}


int yywrap(){

    return 1;

}


Output:

Enter your input (type 'exit' to quit):

1234567

Integer: 1234567

123456.34567

Float: 123456.34567

dfgh

Identifier: dfgh

23456.21

Float: 23456.21


17


===== Page 19 =====


Q12. Design YACC/LEX code to recognize valid arithmetic expression with operators +,-, * and /.


Solution:

Yaac:

% {

    #include <stdio.h>

    #include <stdlib.h>

    void yyerror(const char *msg);

    int yylex();

% }


%token NUMBER

%token PLUS MINUS MUL DIV LPAREN RPAREN EOL


%%


input:

    expression EOL { printf("Valid Expression\n"); }

    | error EOL { printf("Invalid Expression\n"); yyerrok; }

;


expression:

    expression PLUS term

    | expression MINUS term

    | term

    ;


term:

    term MUL factor

    | term DIV factor

    | factor

    ;


factor:

    NUMBER

    | LPAREN expression RPAREN

    ;


%%


void yyerror(const char *msg) {

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

}


int main() {

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

    yyparse();

    return 0;

}


18


===== Page 20 =====


**Lex:**

% {

    #include "12.tab.h"

    #include <ctype.h>

% }


%%


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

[ \t]    ;  // Ignore spaces and tabs

"+"    { return PLUS; }

"-"    { return MINUS; }

"*"    { return MUL; }

"/"    { return DIV; }

"("    { return LPAREN; }

")"    { return RPAREN; }

\n    { return EOL; }

.    { return yytext[0]; } // Catch all for any other character


%%


int yywrap() {

    return 1;

}


19


===== Page 21 =====


Q13. Design YACC/LEX code to evaluate arithmetic expression involving operators +, -* and / without operator precedence grammar &amp; with operator precedence grammar.


Solution:  

Yaac:  

%{  

#include <stdio.h>  

#include <stdlib.h>


int yylex();  

void yyerror(const char *s) {  

    printf("Error: %s\n", s);  

}  

%}


%token NUMBER  

%token PLUS MINUS MULTIPLY DIVIDE  


%left PLUS MINUS  

%left MULTIPLY DIVIDE  


%%


expression:  

    expression PLUS expression  { $$ = $1 + $3; }  

    expression MINUS expression  { $$ = $1 - $3; }  

    expression MULTIPLY expression { $$ = $1 * $3; }  

    expression DIVIDE expression  { $$ = $1 / $3; }  

    '('expression')'   { $$ = $2; }  

    NUMBER   { $$ = $1; }  


%%


int main() {  

    printf("Enter an arithmetic expression (with precedence): ");

    yyparse();  

    return 0;  

}


20


===== Page 22 =====


Lex:

%{

#include "13.tab.h"

%}


%% 

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

[\\n ]    { /* Ignore whitespace */ }

"+"    { return PLUS; }

"-"    { return MINUS; }

"*"    { return MULTIPLY; }

"/"    { return DIVIDE; }

.    { return yytext[0]; }


%% 

int yywrap() {

    return 1;

}

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