Design DFA in LEX Code that accepts the string having even binary number over input alphabet {0,1}
Problem Overview –
Design a DFA in LEX Code that accepts the string having even binary number over input alphabet {0,1}.
Example –
Input : 1010
Output: Accepted
Input : 1001
Output: Not Accepted
Input: 23ab
Output:Invalid
Input:ab345
Output:Invalid
Input:010101
Output:Not Accepted
Approach :
LEX provides us with an INITIAL state by default. So to make a DFA, use this as the initial state of the DFA. We define two more states: A, and DEAD, where the DEAD state would be used if encountering a wrong or invalid input. When the user inputs an invalid character, move to DEAD state, and then print “Invalid”. If the input string ends at A then display the message “Accepted”. Else if the input string ends at state INITIAL then displays the message “Not Accepted”.
Note –
To compile the lex program we need to have a Unix system that has flex installed into it. Then we need to save the file with the .l extension.
For example- filename.l
Then after saving the program closes the lex file and then open the terminal and write the following commands as follows.
lex filename.l
cc lex.yy.c
./a.out
LEX CODE :
%{
%}
%s A DEAD
%%
<INITIAL>0 BEGIN A;
<INITIAL>1 BEGIN INITIAL;
<INITIAL>[^01\n] BEGIN DEAD;
<INITIAL>\n BEGIN INITIAL; {printf("Not Accepted\n");}
<A>0 BEGIN A;
<A>1 BEGIN INITIAL;
<A>[^01\n] BEGIN DEAD;
<A>\n BEGIN INITIAL; {printf("Accepted\n");}
<DEAD>[^\n] BEGIN DEAD;
<DEAD>\n BEGIN INITIAL; {printf("Invalid\n");}
%%
int yywrap()
{
return 1;
}
int main()
{
printf("Enter String\n");
yylex();
return 0;
}
Output :
Enter String
1100
Accepted
1010
Accepted
0001
Not Accepted
abc
Invalid
0101
Not Accepted
Last Updated :
31 Jul, 2021
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