LEX PROGRAM TO COUNT AND REMOVE THE COMMENTS FROM A C PROGRAM

%{
#include<stdio.h>
int count=0,flag=0,m=0;
%}
%%
((\/)(\/).*"\n") {count++;}
("/*")(.*|("\n")*) {flag=1;}
"*/" {if(flag==1){count++;flag=0;}}
([pP][rR][Ii][Nn][Tt][Ff][(].*((\/)(\/)).*) {m++;ECHO;}
([pP][rR][Ii][Nn][Tt][Ff][(].*((\/)(\*)).*((\*)(\/))) {m++;ECHO}
%%
main()
{
yyin=fopen("sample.c","r");
yyout=fopen("sample2.c","w");
yylex();
printf("no of comments=%d m=%d",+count,m);
}


where sample.c is your C program and output will be stored in sample2.c
STEP1:
     YAC program includes three basic parts Definition,rules and subroutines respectively. These are separated by  %% symbol as in the above program.
While compiling entire program will be converted to C program. then it is executed. Definition part will be just placed in the manner how it is present.

STEP2:
     . matches any character other than new line.
     * matches 0 or  more number of preceding character.
   [ ] matches any character within it
    $ matches the end of the line.
    | implies or ex: a|b implies either a or b
   ( ) groups a series of regular expressions

STEP3:
    ((\/)(\/).*"\n") implies--> matches // followed by any number of character or digit and ends with a new line. which is nothing but a single line comment.
     \ used to nullify the effect of / which is present next to i.
     ( ) is used to combine one or more regular expressions.

 ("/*")(.*|("\n")*) matches /* followed by any number of character or digit or any number of new line. which is nothing but a multi-line comment.
        ("/*") implies it must start with /*
        (.*|("\n")*) implies any number of character or digit or any number of new line. ..

STEP4:
([pP][rR][Ii][Nn][Tt][Ff][(].*((\/)(\/)).*) it matches the single line comments if they are present in printf statements. These comments should not be removed. so at the end it will ask you to add into the resulting program.
([pP][rR][Ii][Nn][Tt][Ff][(].*((\/)(\*)).*((\*)(\/))) matches the multi- line comments if they are present in printf statements. These comments should not be removed. so at the end it will ask you to add into the resulting program.

STEP5:
      sample.c is your input file
      sample2.c is your resulting comment free c file. program must be stored with .l extension.
to compile and run in lex follow the commands:
$lex programname.l
$cc lex.yy.c -ll
$./a.out
 
let sample.c be                                      then for an efficient algorithm you
                                                               should get output as:


#include<stdio.h>                                             #include<stdio.h>                
// this is a exaple                                                  void main()
void main()                                                            {
{                                                                             int a,b,c;
int a,b,c;                                                                 c=a+b;
//to add numbers                                                  printf(" // then c=%d ",c);
/* to store                                                             printf(" now /* __*/ c=%d",c);
the result                                                              getch();         
in the c */                                                                }
c=a+b;
printf(" // then c=%d ",c);
printf(" now /* __*/ c=%d",c);
getch();
// end
}

just check whether your program is efficient or not.....