LOGIC: Read the input string. Check whether the string is identifier/ keyword /symbol by using the rules of identifier and keywords using LEX Tool
PROCEDURE: Go to terminal .Open vi editor ,Lex lex.l , cc lex.yy.c , ./a.out
RESOURCE: Linux using Putty
/* program name is lexp.l */
%{
/* program to recognize a c program */
int COMMENT=0;
%}
identifier [a-zA-Z][a-zA-Z0-9]*
%%
#.* { printf("\n%s is a PREPROCESSOR DIRECTIVE",yytext);}
int |float |char |double |while |for |do |if |break |continue |void |switch |case |long |struct |const |typedef |return
|else |goto {printf("\n\t%s is a KEYWORD",yytext);}
"/*" {COMMENT = 1;}
/*{printf("\n\n\t%s is a COMMENT\n",yytext);}*/
"*/" {COMMENT = 0;}
/* printf("\n\n\t%s is a COMMENT\n",yytext);}*/
{identifier}\( {if(!COMMENT)printf("\n\nFUNCTION\n\t%s",yytext);}
{ {if(!COMMENT) printf("\n BLOCK BEGINS");} } {if(!COMMENT) printf("\n BLOCK ENDS");}
{identifier}(\[[0-9]*\])? {if(!COMMENT) printf("\n %s IDENTIFIER",yytext);} ".*\" {if(!COMMENT) printf("\n\t%s is a STRING",yytext);}
[0-9]+ {if(!COMMENT) printf("\n\t%s is a NUMBER",yytext);} {if(!COMMENT) printf("\n\t");ECHO;printf("\n");}
( ECHO;
{if(!COMMENT)printf("\n\t%s is an ASSIGNMENT OPERATOR",yytext);}
<= |>= |< |== |> {if(!COMMENT) printf("\n\t%s is a RELATIONAL OPERATOR",yytext);}
%%
int main(int argc,char **argv)
{
if (argc > 1)
{
FILE *file;
file = fopen(argv[1],"r"); if(!file)
{
printf("could not open %s \n",argv[1]); exit(0);
}
yyin = file;
}
yylex();
printf("\n\n");
return 0;
}
int yywrap()
{
return 0;
}
Input
$vi var.c
#include
main()
{
int a,b;
}
Output
$lex lex.l
$cc lex.yy.c
$./a.out var.c
#include is a PREPROCESSOR DIRECTIVE
FUNCTION
main (
)
BLOCK BEGINS
int is a KEYWORD
a IDENTIFIER
b IDENTIFIER
BLOCK ENDS