Ram Lal Anand College
University of Delhi
Department of Computer Science
Session : 2023 – 2024
Final Practical File
Course Name – B.Sc. (Hons) Computer Science
Semester – 5th
Title of the Paper – System Programming
Paper Code - 32347501
Name of the Student –
Examination Roll No –
Ques-1 Write a Lex program to count the number of lines and
characters in the input file.
Solution-
%option noyywrap
%{
int lines=0;
int characters=0;
%}
%%
. characters++;
\n {lines++;characters++;}
%%
int main()
{
yyin = fopen("input.txt","r");
yylex();
printf("number of lines: %d\n",lines+1);
printf("number of characters: %d\n",characters+1);
return 0;
# input.txt
Output-
Ques-2 Write a Lex program that implements the Caesar cipher: it
replaces every letter with the one
three letters after in alphabetical order, wrapping around at Z. e.g. a is
replaced by d, b by e,
and so on z by c.
Solution -
%{
int rot = 0;
%}
%%
[A-Z] { fprintf(yyout, "%c", (yytext[0] - 'A' + rot) % 26 + 'A'); }
[a-z] { fprintf(yyout, "%c", (yytext[0] - 'a' + rot) % 26 + 'a'); }
. { fprintf(yyout, "%s", yytext); }
%%
int main(void) {
printf("Enter Key (ROT): ");
scanf("%d", &rot);
yyin = fopen("input.txt", "r");
yyout = fopen("output.txt", "w");
yylex();
fclose(yyin);
fclose(yyout);
printf("Successfully changed the value!");
return 0;
}
int yywrap() {
return 1;
}
Input file-
Output-
Output file -
Ques-3 Write a Lex program that finds the longest word (defined as a
contiguous string of upper-
and lower-case letters) in the input.
Solution -
%option noyywrap
%{
#include<string.h>
int longest = 0;
char word[1000];
%}
%%
[a-zA-Z0-9]+ {
if(yyleng>longest){
longest = yyleng;
strcpy(word,yytext);
}
}
[ |\n|\r|\t] { ; }
.{;}
%%
int main(void){
yyin = fopen("text.txt", "r");
yylex();
fclose(yyin);
printf("The longest string is %s \n", word);
printf("Length of a longest string is %d \n",longest);
}
Ques-4 Write a Lex program that distinguishes keywords, integers,
floats, identifiers, operators, and
comments in any simple programming language.
Solution-
%{
int integers = 0;
int floats = 0;
int identifiers = 0;
int operators = 0;
int comments = 0;
%}
%%
[#].* { printf("%s <- preprocessor directive\n", yytext); } // preprocessor
directives
[ |\n|\t] { ; } // whitespaces
[,|;|"("|")"|"{"|"}"|"\["|"\]"] { ; } // brackets, delimiters
"//".* { comments++; printf("%s <- comment\n", yytext); } // single line
comments
[0-9]+ { integers++; printf("%s <- integer\n", yytext); } // integers
[0-9]+("."[0-9]+) { floats++; printf("%s <- float\n", yytext); } // floats
void|int|main|char|for|while|continue|switch|case|break|if|else|
return|true|false { printf("%s <- keyword\n", yytext); } // keywords
"<="|">="|"!
="|"=="|"<"|">"|"&"|"|"|"^"|"<<"|">>"|"~"|"&&"|"||"|"!"|"+
+"|"--"|"="|"+"|"-"|"*"|"/"|"%" { operators++; printf("%s <- operator\
n", yytext); } // operators
[']([^\\\']|\\.)?['] { ; } // characters
["]([^\\\"]|\\.)*["] { ; } // strings
[a-zA-Z_]+[a-zA-Z0-9_]* { identifiers++; printf("%s <- identifier\n",
yytext); } // identifiers
%%
int main() {
yyin = fopen("t1.c", "r");
yylex();
printf("\n");
printf("number of integers: %d\n", integers);
printf("number of floats: %d\n", floats);
printf("number of identifiers: %d\n", identifiers);
printf("number of operators: %d\n", operators);
printf("number of comments: %d", comments);
return 0;
}
int yywrap() {
return 1;
}
Input File-
Output-
Ques-5 Write a Lex program to count the number of identifiers in a C
file.
Solution-
%option noyywrap
%{
int identifiers = 0;
%}
%%
[#].* { ; } // preprocessor directives
[ |\n|\t] { ; } // whitespaces
[,|;|"("|")"|"{"|"}"|"\["|"\]"] { ; } // brackets, delimiters
"//".* { ; } // single line comment
-?[0-9]+("."[0-9]+)? { ; } // numbers
void|int|main|char|for|while|continue|switch|case|break|if|else|return|
true|false { ; } // keywords
"<="|">="|"!="|"=="|"<"|">" { ; } // relational operators
"&"|"|"|"^"|"<<"|">>"|"~" { ; } // bitwise operators
"&&"|"||"|"!" { ; } // logical operators
"++"|"--" { ; } // postfix/prefix operators
"="|"+"|"-"|"*"|"/"|"%" { ; } // other operators
[']([^\\\']|\\.)?['] { ; } // characters
["]([^\\\"]|\\.)*["] { ; } // strings
[a-zA-Z_]+[a-zA-Z0-9_]* { identifiers++; printf("%s <- identifier\n", yytext); } //
identifiers
%%
int main() {
yyin = fopen("text.c", "r");
yylex();
printf("\nnumber of C identifiers: %d\n", identifiers);
return 0;
}
Input file-
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// This is my code
void loop()
{
int i, j = 7;
for (int i = 0; i < j; i++)
{
printf("%d. Hello\n", (j + 1));
}
}
int main()
{
double a = -3.14;
char at = '@', tab = '\t';
loop();
return 0;
}
Output-
Ques-6 Write a Lex program to count the number of words, characters, blank
spaces and lines in a C
file.
Solution-
%{
int words = 0;
int lines = 0;
int spaces = 0;
int characters = 0;
%}
%%
[^ \t\n,\.:;]+ { words++; characters += yyleng; }
[\n] { lines++; characters += yyleng; }
[ |\t] { spaces++; characters += yyleng; }
. { characters++; }
%%
int main() {
yyin = fopen("text.c", "r");
yylex();
printf("number of words: %d\n", words);
printf("number of blank spaces: %d\n", spaces);
printf("number of lines: %d\n", lines);
printf("number of characters: %d\n", characters);
return 0;
}
int yywrap() {
return 1;
}
Input file/code-
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void loop()
{
int i, j = 5;
for (int i = 0; i < j; i++)
{
printf("%d. Hi\n", (i + 1));
}
}
int main()
{
double a = -3.14;
char at = '@', tab = '\t';
loop();
return 0;
}
Ques-7 Write a Lex specification program that generates a C program
which takes a string “abcd”
and prints the following output.
abcd
abc
ab
a
Solution-
%option noyywrap
%{
#include <stdio.h>
%}
%%
a|ab|abc|abcd { printf("%s\n", yytext); REJECT; }
.|\n { ; }
%%
int main() {
yyin = fopen("input.txt", "r");
yylex();
return 0;
}
Input file-
Output-
Ques-8 A program in Lex to recognize a valid arithmetic expression.
Solution-
%{
#include <stdio.h>
int brackets = 0,
operators = 0,
numbersOridentifiers = 0,
flag = 0;
%}
%%
[a-zA-Z_]+[a-zA-Z0-9_]* { numbersOridentifiers++; }
-?[0-9]+("."[0-9]+)? { numbersOridentifiers++; }
[+|\-|*|/|=|\^|%] { operators++; }
"(" { brackets++; }
")" { brackets--; }
";" { flag = 1; }
.|\n { ; }
%%
int main() {
printf("\nEnter Arithmetic Expression: ");
/* yyin = fopen("input.txt", "r"); */
yylex();
if (
(operators + 1) == numbersOridentifiers
&& brackets == 0 && flag == 0
){
printf("Valid Expression\n");
} else {
printf("Invalid Expression\n");
}
return 0;
}
int yywrap() {
return 1;
}
Output
Ques-9 writes a yacc program to verify an expression as valid or not.
Solution-
first.y
%{
#include<stdio.h>
#include<stdlib.h>
int flag = 0;
%}
%token ID
%token NUMBER
%left '+' '-'
%left '*' '/' '%'
%%
stmt : expr {
printf("Result=%d \n",$$);
return 0;
};
expr : expr'+'expr {$$ = $1 + $3;} |
expr'-'expr {$$ = $1 - $3;} |
expr'*'expr {$$ = $1 * $3;} |
expr'/'expr {$$ = $1 / $3;} |
'('expr')' {$$ = $2;} |
ID {$$ = $1;} |
NUMBER {$$ = $1;}
;
%%
int main(){
printf("enter expr: \n");
yyparse();
if(flag == 0){
printf("Valid expression");
}
}
int yyerror(){
printf("Error \n");
flag = 1;
}
yacc.l
%{
#include<stdio.h>
#include "first.tab.c"
extern int yylval;
%}
%%
[0-9]+ {
yylval = atoi(yytext);
return NUMBER;
}
[a-zA-Z]+ {
yylval = yytext;
return ID;
}
[\n] {return 0;}
. return yytext[0];
%%
int yywrap(){
return 1;
}
Que10. A Program in YACC which recognizes a valid variable
which starts with letter followed by a digit. The letter should be in
lowercase only.
#p10.l
%{
#include "p10.tab.c"
%}
%%
[a-zA-Z_][a-zA-Z_0-9]* return letter;
[0-9] return digit;
. return yytext[0];
\n return 0;
%%
int yywrap()
return 1;
#P10.y
%{
#include<stdio.h>
int valid=1;
%}
%token digit letter
%%
start : letter s
s: letter s
| digit s
%%
int yyerror()
printf("\nIts not a identifier!\n");
valid=0;
return 0;
}
int main()
printf("\nEnter a name to tested for identifier ");
yyparse();
if(valid)
printf("\nIt is a identifier!\n");
}
Que11. A Program in YACC to evaluate an expression (simple
calculator program for addition and subtraction, multiplication,
division).
#p11.l
%{
#include <stdio.h>
#include "p11.tab.c"
extern int yylval;
%}
%%
[0-9]+ {
yylval = strtol(yytext,NULL,0);
return NUMBER;
}
\n {return 0;}
. {return yytext[0];}
%%
int yywrap() {
return 1;
}
#p11.y
%{
#include <stdio.h>
#include <stdlib.h>
%}
%token NUMBER
%left '+' '-'
%left '*' '/'
%left '(' ')'
%%
stmt:e {printf("\nresult : %d",$$);}
e: e '+' e {$$ = $1 + $3;}
| e '-' e {$$ = $1 - $3;}
| e '*' e {$$ = $1 * $3;}
| e '/' e {$$ = $1 / $3;}
| '(' e ')' {$$ = $2;}
| NUMBER ;
%%
int main(){
printf("Enter expression (+ / * - %) : ");
yyparse();
printf("\nValid expression :)");
return 0;
}
int yyerror(){
printf("\nInvalid expression :(");
return 0;
}
Que12. Program in YACC to recognize the strings “ab”, “aabb”,
”aaabbb”,… of the language (𝑎𝑛 𝑏𝑛 , n>=1).
#p12.l
%{
#include "p12.tab.c"
%}
%%
[aA] {return A;}
[bB] {return B;}
\n {return NL;}
. {return yytext[0];}
%%
int yywrap(){
return 1;
}
#p12.y
%{
#include<stdio.h>
#include<stdlib.h>
%}
%token A B NL
%%
stmt: S NL { printf("valid string\n"); exit(0); } ;
S: A S B | ;
%%
int yyerror(char *msg) {
printf("invalid string\n");
exit(0);
}
main() {
printf("enter the string\n");
yyparse();
}
Que13. Program in YACC to recognize the language (𝑎𝑛𝑏 ,
n>=10). (Output to say input is valid or not)
#p13.l
%{
#include "p13.tab.c"
extern int yylval;
%}
A [a]{10,}
B [b]
%%
{A} {yylval=yytext[0];return A;}
{B} {yylval=yytext[1];return B;}
\n {return 0;}
. {return yytext[0];}
%%
int yywrap(){
return 1;
}
#p13.y
%{
#include<stdio.h>
#include<stdlib.h>
int yylex(void);
%}
%token A B
%%
expr: s B {printf("\n valid string");};
s:sA|A;
%%
int main(){
printf(" Enter the string \n");
yyparse();
return 0;
}
int yyerror(){
printf(" Invalid: Not a part of the language - a^n b \n");
}
