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LEX Code for Tokenizing (Identify and print OPERATORS, SEPARATORS, KEYWORDS, IDENTIFIERS) for the given C fragment

In this article, we going to learn how to create LEX program to analysis among the given C program which are operators, separators, keywords, identifiers and print on the console?
Submitted by Ashish Varshney, on March 24, 2018

C code

    int p=1,d=0,r=4;
    float m=0.0, n=200.0;
    while (p <= 3)
    { 
	    if(d==0)
		    { m= m+n*r+4.5; d++; }
	    else
		    { r++; m=m+r+1000.0; }	
	    p++; 
    }

For achieve to this task we create some rules in rule section in the code.

/*Definition Section*/

%{
#include<stdio.h>
%}

/*Rule Section*/

%%
/*Check the token, if token is match with pattern 
then it will print KEYWORD.*/
auto|double|int|struct|break|else|long|switch
|case|enum|register|typedef|char|extern|return
|union|continue|for|signed|void|do|if|static
|while|default|goto|sizeof|volatile|const|float
|short     {ECHO; printf("\nKEYWORD\n");} 						
/*Check the token, if token is match with pattern 
then it will print SEPERATOR.*/
[{};,()]   {ECHO; printf("\tSEPERATOR\t");}						
/*Check the token, if token is match with pattern 
then it will print OPERATOR.*/
[+-/=*%]   {ECHO; printf("\tOPERATOR\t");}						
/*Check the token, if token is match with pattern 
then it will print IDENTIFIER.*/
([a-zA-Z][0-9])+|[a-zA-Z]* {ECHO; printf("\tIdentifier\t");}    
/*No action*/
.|\n ; 															
%%

/*call the yywrap function*/
int yywrap()								
{
return 1;
}


/*Auxiliary function*/
/*Driver function*/

int main(void)
{
/*call the yylex function.*/
yylex();
return 0;
}

Output