Lex and Yacc in Windows 7 - Compile and Run

Hi Friend,
I was in search for a long time to get a platform in windows-7 to run lex and Yacc ,for academic purposes. Many of my friends also had the same problem and often forced to choose Linux only for merely executing Lex & Yacc programs..!!!

At last, I found one solution and its my pleasure to share it with all of you.!!  :)

Its very simple.You need to download two very small files.
You have to download two executable( i.e.,   .exe files). In total,its size may have about 370KB.

To download them click the links below.

Link 1:   Flex

Link 2:  Bison

Save both files in same place. ( I did in D: --> Flex)
Keep the lex program to be compiled also in same place.

Now open command prompt--> reach your directory through command prompt.

To compile, type command 
                flex <filename> (eg:- flex myflex.l)

If your program is error-free, lex.yy.c will be generated.

We can compile this C file with any C compiler available (eg: Turbo C)

and generate yy.lex.exe

Now just run yy.lex.exe. Its your lexical analyser..!!!

I hope this post was useful for you.!!
Please comment your feedback here.!!
Thank You.!!  :)

Read more »

Calculator using YACC program

Here is the Yacc program implementing a simple calculator:

%{
#include<stdio.h>
#include<ctype.h>
%}
%token num
%left '+''-'
%left '*''/'
%right '^'
%%
s:e'\n'{printf("%d",$1);}
e:    e '+' e{$$=$1+$3;}
 |e '-' e{$$=$1-$3;}
 |e '*' e{$$=$1*$3;}
 |e '/' e{$$=$1/$3;}
 |e '^' e {
  int i,j=$1;
  for(i=1;i<$3;i++)
  {
  j=j*$1;
  $$=j;
  }
  }
 |'('e')'{$$=$2;}
 |num1;
num1:num1 num{$$ = $1*10 + $2;}
 |num
 ;
%%
yylex()
{
int c;
c=getchar();
if(isdigit(c))
{
yylval=c-'0';
return num;
}
return c;
}
int main()
{
yyparse();
return 1;
}
int yyerror()
{
return 1;
}
int yywrap()
{
return 1;
}



Illustration:

Let the Input be 2+5

Moving from first definition s:e'\n'
s  --> move to DEF(e)
e: e '+' e is selected. Evaluate first 'e' ie e-->num1
num1 extracts the token (i.e, number here 2 is extracted and stored in $1)
Then '+' is extracted and stored in $2.
Then move to e--> num1, thus 5 is  extracted and stored  in $3.
Now add them and store result in $$.

Go back to S: e'\n' and print result (which is 'e' here..!!)


If you have any doubt regarding this post feel free to comment here.
Thank U..!!

For more Yacc programs click here..!!

Read more »

YACC program to convert infix

%{#include<stdio.h>
#include<ctype.h>
%}
%token num
%left '+''-'
%left '*' '/'
%%
s:e'\n'{}
e:e'+'e{printf("+");}
|e'-'e{printf("-");}
|e'/'e{printf("/");}
|e'*'e{printf("*");}
|num1{printf("%d",$1);}
num1:num1 num {$$=$1*10+$2;}
|num
;
%%
yylex()
{
 int c;
 c=getchar();
if(isdigit(c))
{ yylval=c-'0';
 return num;
}return c;
}
int main()
{
 yyparse();
return 1;
}
int yyerror()
{
return 1;
}
int yywrap()
{
 return 1;
}

Read more »

Yacc program to evaluate POSTFIX expression

%{#include<stdio.h>
#include<ctype.h>
%}
%token num
%left '+''-'
%left '*' '/'
%right '^'
%%
s:e'\n'{printf("\n%d",$1);}
e:e e'+'{$$=$1+$2;}
|e e'-'{$$=$1-$2;}
|e e'*'{$$=$1*$2;}
|e e'/'{$$=$1/$2;}
|num
;
%%
yylex()
{
int c;
c=getchar();
if(isdigit(c))
{ yylval=c-'0';
 return num;
}return c;
}
int main()
{
 yyparse();
return 1;
}
int yyerror()
{
return 1;
}
int yywrap()
{
 return 1;
}

Illustraion:

Evaluation of postfix expression can be done very easily.

34+
3--> store value in $1
4--> store value in $2
+--> add $1 and $2 and store result in $$

For more Yacc programs click here..!!

Read more »