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;
}