1. Write a Lex program to count the number of lines and

characters in the input file.

%{

int lines=0, words=0, ch=0, bl=0;

%}

word [^ \n\t]+

eol \n

%%

{word} {words++; ch+=yyleng;}

" " bl++;

{eol} lines++;

. {ch++;} /* any char except new line */

%%

int main(void)

{

yylex();

printf( " lines = %d words = %d characters = %d blanks = %d \n " ,

lines , words , ch , bl );

}

Output:

$ lex lex1.l

$ cc lex.yy.c -ll

$ ./a.out < names

lines = 3 words = 3 characters = 22 blanks = 0

$ cat names

Lakshya

Sachin

Udheeshen

2. Write a Lex program that implements the Caesar cipher:

it replaces every letter with the one three letters after

in in alphabetical order, wrapping around at Z.

e.g. a is replaced by d, b by e, and so on z by c

%%

[a-wA-W] printf ("%c", yytext[0] + 3);

[x-zX-Z] printf("%c", yytext[0] - 23);

%%

int main(void)

{

yylex();

}

Output:

$ lex lex2.l

$ cc lex.yy.c -ll

$ ./a.out

This is a Lex program

Wklv lv d Oha surjudp

XYZ

ABC

3. Write a Lex program that finds the longest word (defined

as a contiguous string of upper and lower case letters) in

the input.

%{ #include<string.h>

int longest=0; char longword[60];

%}

%%

[a-zA-Z]+ { if( yyleng > longest )

{ longest=yyleng;

strcpy(longword, yytext);

}

}

.

\n

%%

int main( void )

{

yylex();

printf( "Longest word is \" %s \" , having %d characters\n" ,

longword, longest);

}

Output:

$ lex lex3.l

$ cc lex.yy.c -ll

$ ./a.out

This is Lex programming.

Longest word is " programming " , having 11 characters

4. Write a Lex program that distinguishes keywords,

integers, floats, identifiers, operators, and comments in

any simple programming language.

%{#include<math.h>

%}

DIGIT [0-9]

ID [a-z][a-z0-9]*

COMMENT \/\*.*\*\/

%%

{DIGIT}+ { printf("\nAn Integer: %s ", yytext, atoi(yytext));

}

{DIGIT}+"."{DIGIT}* {printf("\nA Float: %s ", yytext, atof(yytext));}

("void")|("int")|("char")|("if")|("else")|("for")|("while")|("do")|("

exit")|("cout")|("cin")|("main")|("break")|("continue") {printf("\nA

Keyword: %s",yytext); }

{ID} {printf("\nAn Identifier: %s",yytext);}

{COMMENT} printf("\nComments are: %s",yytext);

[+|-|*|/] printf("\nAn Operator: %s", yytext);

[\t\n]+

%%

int main()

{ yylex();

return 0;

}

$ lex abc.l

$ cc lex.yy.c -ll

$ ./a.out

/*this is a program to swap two num*/ void swap() { int a=3; b=6;

temp=a; a=b; b=temp; cout<<a<<b;}

Comments are: /*this is a program to swap two num*/

A Keyword: void

An Identifier: swap() {

A Keyword: int

An Identifier: a=

An Integer: 3 ;

An Identifier: b=

An Integer: 6 ;

An Identifier: temp=

An Identifier: a;

An Identifier: a=

An Identifier: b;

An Identifier: b=

An Identifier: temp;

A Keyword: cout<<

An Identifier: a<<

An Identifier: b;}

5. Write a LEX program to count the number of identifiers

in a C file.

%{ #include<math.h>

int count=0;

%}

Digit [0-9]*

Id [a-z][a-z0-9]*

Datatype [ "int" | "char" | "float" | "long" | "double" | "bool" ]

%%

{Datatype}" "{Id}"="{Digit} | {Id}";" count++;

{Datatype}" "{Id}";" count++;

.

\n

%%

int main(void)

{

yylex();

printf("Number of Identifiers : %d\n", count);

return 0;

}

Output:

$ lex lex5.l

$ cc lex.yy.c -ll

$ ./a.out < t1.C

$ ./a.out < t1.C

Number of Identifiers : 5

$ cat t1.C

/*this is a program to swap two num*/

void swap()

{

int a=3;

b=6;

temp=a;

a=b;

b=temp;

cout<<a<<b;

}

6. Write a LEX program to count the number of words,

characters, blank spaces and lines in a C file.

%{

int ch=0, bl=0, line=0, wr=0;

%}

%%

[\n] {line++; wr++;}

[\t] {bl++; wr++;}

" " {bl++; wr++;}

[^ \n\t] {ch++;}

%%

int main(void)

{

FILE *fp;

char file[55];

printf(" \n Enter a file name: ");

scanf("%s", file);

fp= fopen(file, "r");

yyin=fp;

yylex();

printf(" Characters= %d \n blanks= %d \n lines=%d \n words=%d", ch,

bl, line, wr);

return 0;

}

Output:

$ lex lex6.l

$ cc lex.yy.c -ll

$ ./a.out < t1.c

Enter a file name: Characters= 76

blanks= 29

lines=10

words=39lakshya@lakshya-Aspire-4736Z:~/practicals$ cat t1.c

/*this is a program to swap two num*/

void swap()

{

int a=3;

b=6;

temp=a;

a=b;

b=temp;

cout<<a<<b;

}

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

%%

a|ab|abc|abcd printf("%s\n",yytext);REJECT;

.|\n

%%

int main(void)

{

yylex();

return 0;

}

Output:

$ lex lex7.l

$ cc lex.yy.c -ll

$ ./a.out

abcd

abcd

abc

ab

a

8. A program in LEX to recognize a valid arithmetic

expression.