Recognize arithematic expression

Lex program

%{
#include <stdio.h>
#include "y.tab.h"
%}
number        [0-9]+
flot         [0-9]*"."[0-9]+
identifier    [a-zA-Z][a-zA-Z0-9]*
errr     [0-9][a-zA-Z0-9]*
%%
{number} {    return number;    }
{flot} {    return number;    }
{identifier} {    return identifier;    }
{errr} {    return err; }
[ \t]+
\n  {    return(0); }
.    {    return (int) yytext[0];}
%%

Yacc program

%{
#include <stdio.h>
int f=0;
%}
%token number identifier err
%%
input:    /* empty string */
          | input exp
       |error {f=1;}
       ;
exp:      number
       |identifier
           | exp '+' exp            
           | exp '-' exp           
           | exp '*' exp            
           | exp '/' exp            
           | '-' exp 
           | exp '^' exp  
           | '(' exp ')'
     ;
%%
int main()
{
         printf("\nEnter an arithmetic expression:\n\n");
         yyparse();
         if(f==0)
            printf("Valid Expression \n");
         else
            printf("Invalid Expression\n");
         return 0;
}
int yywrap()
{
           return 1;
}
int yyerror(char *mes) {printf("%s\n", mes);}

Recognize (0+1)*000(0+1)*

%{
#include <stdio.h>
int count=0;
%}
str     [0-1]*"000"[0-1]*
err     [a-zA-Z0-9]+
%%
{str} {    count++; }
{err}
%%
int main()
{
       yylex();
       printf("The pattern (0+1)*000(0+1)* found %d times \n",count);
}
int yywrap()
{
       return 1;
}

Recognize aa(a+b)*bb

%{
#include <stdio.h>
int count=0;
%}
str     "aa"[ab]*"bb"
err     [a-zA-Z0-9]+
%%
{str} {    count++; }
{err}
%%
int main()
{
       yylex();
        printf("The pattern aa(a+b)*bb found %d times \n",count);
}
int yywrap()
{
        return 1;
}

Implement (a+b+c)*abc using transition table

#include<stdio.h>
#include<string.h>
int main()
{
     char str[50],input[15],inpstate[15],outstate[15],state='A';
     int i=0,j;
     strcpy(input,"abcabcabcabc");
     strcpy(inpstate,"AAABBBCCCDDD");
     strcpy(outstate,"BAABCABADBAA");
     printf("\nEnter the string:-  ");
     gets(str);
     while(str[i]!='\0')
     {
          for(j=0;j<12;j++){
         if(inpstate[j]==state && input[j]==str[i]){
              state=outstate[j];
              break;
          }
           }
          if(j==12){
          state='E';
          break;
        }
        i++;
     }
     if(state=='D')
          printf("\nValid String \n");
     else
          printf("\nInvalid String \n");
     return 0;
}

Count statements, identifiers, operators, keywords, integers

%{
#include <stdio.h>
int no_of_stat=0;
int no_of_id=0;
int no_of_ar=0;
int no_of_re=0;
int no_of_key=0;
int no_of_int=0;
%}
digit [0-9]+
key "int"|"float"|"while"|"if"|"printf"|"for"
id [a-zA-Z][a-zA-Z0-9]*
arop "+"|"-"|"*"|"/"|"%"|"++"|"--"
relop "=="|">"|">="|"<="|"!="|"<"
semi ";"[ ]*"\n"

%%
{digit} { no_of_int++; }
{key} { no_of_key++; }
{id} { no_of_id++; }
{arop} { no_of_ar++; }
{relop} { no_of_re++; }
{semi} { no_of_stat++; }
.
%%
int main()
{
   char inp[20];
    printf("Enter the input file name ");
    scanf("%s",inp);
    yyin=fopen(inp,"r");
    yylex();
    printf("\n no of C statements:- %d",no_of_stat);
    printf("\n no of identifiers:- %d",no_of_id);
    printf("\n no of arithmetic operators :- %d",no_of_ar);
    printf("\n no of relational operators:- %d",no_of_re);
    printf("\n no of keywords:- %d",no_of_key);
    printf("\n no of integers:- %d\n",no_of_int);
}
int yywrap()
{
    return 1;
}

Check for keywords, identifiers, numbers and operators

%{
#include <stdio.h>
char output[500];
%}
digit [0-9]+
flot [0-9]*"."[0-9]+
key "int"|"float"|"while"|"if"|"printf"
id [a-zA-Z][a-zA-Z0-9]*
op "+"|"-"|"*"|"/"|"%"|"=="|">"|">="|"="
err [0-9][a-zA-Z0-9]*
%%
{digit} { sprintf(output,"%snumber ",output); }
{flot} { sprintf(output,"%sflonumber ",output); }
{key} { sprintf(output,"%skeyword ",output); }
{id} { sprintf(output,"%sidentifier ",output); }
{op} { sprintf(output,"%soperator ",output); }
{err} { sprintf(output,"%sinvalid ",output); }
[ \t\n{}();:,]+ { sprintf(output,"%s%s",output,yytext); }
%%
int main()
{
    char inp[20];
    printf("Enter the input file name ");
    scanf("%s",inp);
    yyin=fopen(inp,"r");
    yylex();
    printf("%s",output);
}
int yywrap()
{
    return 1;
}

Binary number with two concecutive zeros

DFA

#include<stdio.h>
int main(){
  int i=0,state=0;
 char str[100];
   printf("\nEnter a binary number:- ");
   gets(str);
 while(str[i]!='\0'){
  switch(str[i]){
    case '0':if(state!=2)
    state++;
     break;
    case '1':if(state==1)
    state=0;
     break;
    default:state=5;
     i=strlen(str)-1;
  }
  i++;
 }
 if(state==2)
  printf("\nValid String\n");
 else 
  printf("\nIn Valid String\n");
 return 0;
}