2. Develop a lexical analyzer to recognize a few patterns in C. (Ex. identifiers, constants, comments, operators etc.)

Ex. No: 2

Date:

Develop a lexical analyzer to recognize a few patterns in C. (Ex. identifiers, constants, comments, operators etc.)

AIM:

To Write a C program to develop a lexical analyzer to recognize a few patterns in C.

ALGORITHM:

1. Start the program

2. Include the header files.

3. Allocate memory for the variable by dynamic memory allocation function.

4. Use the file accessing functions to read the file.

5. Get the input file from the user.

6. Separate all the file contents as tokens and match it with the functions.

7. Define all the keywords in a separate file and name it as key.c

8. Define all the operators in a separate file and name it as open.c

9. Give the input program in a file and  name it as input.c

10. Finally print the output after recognizing all the tokens.

11. Stop the program.

PROGRAM

#include<stdio.h>

#include<conio.h>

#include<ctype.h>

#include<string.h> void main()

{

FILE *fi,*fo,*fop,*fk; int flag=0,i=1;

char c,t,a[15],ch[15],file[20]; clrscr();

printf("\n Enter the File Name:"); scanf("%s",&file);

fi=fopen(file,"r"); fo=fopen("inter.c","w");

fop=fopen("Oper.c","r");

fk=fopen("key.c","r"); c=getc(fi); while(!feof(fi))

{

if(isalpha(c)||isdigit(c)||(c=='['||c==']'||c=='.'==1)) fputc(c,fo);

else

{

if(c=='\n') fprintf(fo,"\t$\t");

else fprintf(fo,"\t%c\t",c);

}

c=getc(fi);

}

fclose(fi); fclose(fo);

fi=fopen("inter.c","r"); printf("\n Lexical Analysis"); fscanf(fi,"%s",a);

printf("\n Line: %d\n",i++); while(!feof(fi))

{

if(strcmp(a,"$")==0)

{

printf("\n Line: %d \n",i++); fscanf(fi,"%s",a);

}

fscanf(fop,"%s",ch);

while(!feof(fop))

{

if(strcmp(ch,a)==0)

{

fscanf(fop,"%s",ch); printf("\t\t%s\t:\t%s\n",a,ch); flag=1;

}

fscanf(fop,"%s",ch);

}

rewind(fop); fscanf(fk,"%s",ch);

while(!feof(fk))

{

if(strcmp(ch,a)==0)

{

fscanf(fk,"%k",ch); printf("\t\t%s\t:\tKeyword\n",a); flag=1;

}

fscanf(fk,"%s",ch);

}

rewind(fk); if(flag==0)

{

if(isdigit(a[0])) printf("\t\t%s\t:\tConstant\n",a);

else

printf("\t\t%s\t:\tIdentifier\n",a);

}

flag=0; fscanf(fi,"%s",a);

}

getch();

}

Key.c

int void main char if

for

while else printf scanf FILE

include stdio.h conio.h iostream.h

Oper.c

( open para

) closepara

{ openbrace

} closebrace

< lesser

> greater

" doublequote ' singlequote

: colon

; semicolon

# preprocessor

= equal

== asign

% percentage

^ bitwise

& reference

* star

+ add

- sub

\ backslash

/ slash

INPUT.c

#include "stdio.h"

#include "conio.h" void main()

{

int a=10,b,c; a=b*c; getch();

}

OUTPUT:

Line:1

# : preprocessor include : Identifier &quot; : doublequote stdio.h : Keyword &quot; : doublequote

Line: 2

# : preprocessor include : Identifier &quot; : doublequote conio.h : Keyword &quot; : doublequote

Line: 3

void : Keyword main : Keyword ( : open

) : closepara

Line: 4

{ : openbrace

Line: 5

int : Keyword a : Identifier

= : equal

10 : Constant

, : Identifier b : Identifier

, : Identifier c : Identifier

; : semicolon

Line: 6

a : Identifier

= : equal

b : Identifier

* : star

c : Identifier

; : semicolon

Line: 7

getch : Identifier ( : open

) : closepara

; : semicolon

Line: 8

} : closebrace

RESULT:

Thus the above program for developing the lexical the lexical analyzer and recognizing the few pattern s in C is executed successfully and the output is verified