Regular expression

#include <stdio.h>
#include<string.h>


int main(){
    int i,state_a=0,state_b,state_n;
    char s[100];
    printf("Enter your string");
    gets(s);
    int len=strlen(s);

    for(i=0;i<len;i++){
        if(s[i]=='a')
        {
            state_a=state_a+1;
        }
        else if(s[i]=='b'){
            if((s[i+1])=='a'){
                state_n=1;
                break;
            }
            else(state_b=state_b+1);
        }
        else if(s[i]!='a' || s[i]!='b')
        {
            state_n=1;
            break;
        }
        else
            continue;
    }
    if(state_a==len)
    {
        printf("the string is not recognised");
    }
    else if(state_b==len)
    {
        printf("the string is recognised under the 'a*b+'");
    }
    else if(state_n==1){
         printf("the string is not recognised");
    }
    else
    {
        printf("the string is recognised under the 'a*b+'");
    }

    getch();
}