strmtch

#include<stdio.h>

void main()

{

    char s[20],c;
    int len,state=0,i;
    printf("Enter a string:\n");
    scanf("%s",s);
    len=strlen(s);
    for(i=0;i<len;i++){
        switch(state){

        case 0:
            c=s[i];
            if(c=='a'){
                state=1;
            }
            else if(c=='b'){
                state=2;
            }
            else{
                state=6;
            }
            break;

        case 1:
            c=s[i];
            if(c=='a'){
                state=3;
            }
            else if(c=='b'){
                state=4;
            }
            else{
                state=6;
            }
            break;

        case 2:
            c=s[i];
            if(c=='a'){
                state=6;
            }
            else if(c=='b'){
                state=2;
            }
            else{
                state=6;
            }
            break;

        case 3:
            c=s[i];
            if(c=='a'){
                state=3;
            }
            else if(c=='b'){
                state=2;
            }
            else{
                state=6;
            }
            break;

        case 4:
            c=s[i];
            if(c=='a'){
                state=6;
            }
            else if(c=='b'){
                state=5;
            }
            else{
                state=6;
            }
            break;

        case 5:
            c=s[i];
            if(c=='a'){
                state=6;
            }
            else if(c=='b'){
                state=2;
            }
            else{
                state=6;
            }
            break;

        case 6:
            printf("%s is not recognised.\n",s);
            exit(0);

        }

    }

    if(state==1){
        printf("\n%s is accepted under rule 'a'\n",s);
    }
    else if((state==2)||(state==4)){
        printf("\n%s is accepted under rule 'a*b+'\n",s);
    }
    else if(state==5){
        printf("\n%s is accepted under rule 'abb'\n",s);
    }
    return 0;
}