expt2-toc-dfa

//#include "stdafx.h"
#include<iostream>
#include<string.h>
using namespace std;
int main()
{
    char a[13];
    int x,state=0,i;
    for(i=0;i<13;i++)
    {
        a[i]=0;
    }
    cout<<"enter the string\n";
    cin>>a;
    i=0;
    while(a[i]!=0)
    {
        switch(state)
        {
        case 0:
            if(a[i]=='a')
            {
                state=1;
            }
            else if((a[i]=='b')||(a[i]=='c'))
            {
                state=0;
            }
            //flag=0;
            break;
        case 1:
            if(a[i]=='b')
            {   state=2;
            }
            else if(a[i]=='c')
            {   state=0;}
            else if(a[i]=='a')
            {state=1;}
            //flag=0;
            break;
        case 2:
            if(a[i]=='c')
            {
             state=3;
             //flag=1;
            }
            else if(a[i]=='a')
            {state=1;
            //flag=0;
            }
            else if(a[i]=='b')
            {state=0;
            //flag=0;
            }

            break;
        case 3:
            if(a[i]=='a')
            {   state=4;
            }
            else if((a[i]=='b')||(a[i]=='c'))
            {   state=4;
            }
            //flag=1;
            break;
        case 4:
            if(a[i]=='b')
                state=5;
            else if(a[i]=='c')
                state=3;
            else if(a[i]=='a')
                state=4;
            //flag=1;
            break;
        case 5:
            if(a[i]=='c')
            {state=0;}
            else if(a[i]=='b')
            {   state=3;}
            else if(a[i]=='a')
            {state=4;}
            //flag=1;
            break;
        default:
            cout<<"error..........................";
            break;
        }
            i++;

    }
    cout<<"\n\n";
        if((state==3)||(state==4)||(state==5))
        {
        cout<<"valid string";
        }
        else
        {
        cout<<"invalid string";
        }
    return 0;
}