Problem A (String starting with 0 and ending with 1)

bool ex3_5(const char s[])
{
	int state = 0;
	for(int i=0;s[i] != TERM; i++)
	{
		if(TRACE)cout << state;
		switch(state)
		{
		case 0:
			if(s[i] == '0')state = 2;
			else if(s[i] == '1')state = 1;
			break;
		case 1:
			if(s[i] == '0')state = 1;
			else if(s[i] == '1')state = 1;
			break;
		case 2:
			if(s[i] == '0')state = 2;
			else if(s[i] == '1')state = 3;
			break;
		case 3:
			if(s[i] == '0')state = 2;
			else if(s[i] == '1')state = 3;
			break;
		}
		if(TRACE)cout << " " << s[i] << " " << state << endl;
	}
	return state==3;  // returns true, if state == 3, else false 
}

--

Problem B (String containing 10 but not 101)

bool ex3_9(const char s[])
{
	int state = 0;
	for(int i=0;s[i] != TERM; i++)
	{
		if(TRACE)cout << state;
		switch(state)
		{
		case 0:
			if(s[i] == '0')state = 0;
			else if(s[i] == '1')state = 1;
			break;
		case 1:
			if(s[i] == '0')state = 2;
			else if(s[i] == '1')state = 1;
			break;
		case 2:
			if(s[i] == '0')state = 4;
			else if(s[i] == '1')state = 3;
			break;
		case 3:
			if(s[i] == '0')state = 3;
			else if(s[i] == '1')state = 3;
			break;
		case 4:
			if(s[i] == '0')state = 4;
			else if(s[i] == '1')state = 5;
			break;
		case 5:
			if(s[i] == '0')state = 6;
			else if(s[i] == '1')state = 5;
			break;
		case 6:
			if(s[i] == '0')state = 4;
			else if(s[i] == '1')state = 3;
			break;
		}
		if(TRACE)cout << " " << s[i] << " " << state << endl;
	}
	if (state==2 || state == 4 || state == 5 || state == 6)
	    return true;
	else
	    return false;
}
---

Problem C (password)

bool ispassword(const char s[])
{
	int state = 0;
	for(int i=0;s[i] != TERM; i++)
	{
		if(TRACE)cout << state;
		switch(state)
		{
		case 0:
			if(islower(s[i]))state = 0;
			else if(isupper(s[i]))state = 1;
            else if(ispunct(s[i]))state = 2;
            else state = 4;
			break;
		case 1:
			if(islower(s[i]))state = 1;
			else if(isupper(s[i]))state = 1;
			else if(ispunct(s[i]))state = 3;
			else state = 4;
			break;
		case 2:
			if(islower(s[i]))state = 2;
			else if(isupper(s[i]))state = 3;
			else state = 4;
			break;
		case 3:
			if(islower(s[i])) state = 3;
			else if(isupper(s[i])) state = 3;
			else if(ispunct(s[i])) state = 4;
		    else state = 4;
			break;
		case 4:
		    // fail state
		    state = 4;
			break;
		}
		if(TRACE)cout << " " << s[i] << " " << state << endl;
	}
	return state==3;  // returns true, if state == 3, else false 
}

----

Problem D (email):

bool isemail(const char s[])
{
	int state = 0;
	for(int i=0;s[i] != TERM; i++)
	{
		if(TRACE)cout << state;
		switch(state)
		{
		case 0:
		    if (isdigit(s[i])) state = 1;
		    else if (isalpha(s[i])) state = 1;
		    else state = -1;
			break;
		case 1:
		    if ((int)s[i] == (int)'.') state = 4;
		    else if ((int)s[i] == (int)'-') state = 4;
		    else if ((int)s[i] == (int)'_') state = 4;
		    else if ((int)s[i] == (int)'@') state = 3;
		    else if (isalnum(s[i])) state = 2;
			else state = -1;
			break;
		case 2:
		    if ((int)s[i] == (int)'.') state = 4;
		    else if ((int)s[i] == (int)'-') state = 4;
		    else if ((int)s[i] == (int)'_') state = 4;
		    else if ((int)s[i] == (int)'@') state = 3;
			else if (isalnum(s[i])) state = 2;
			else state = -1;
			break;
		case 3:
		    if ((int)s[i] == (int)'.') state = -1;
		    else if ((int)s[i] == (int)'-') state = -1;
		    else if ((int)s[i] == (int)'_') state = -1;
            else if (isalnum(s[i])) state = 5;
            else state = -1;
			break;
		case 4:
		    if ((int)s[i] == (int)'.') state = -1;
		    else if ((int)s[i] == (int)'-') state = -1;
		    else if ((int)s[i] == (int)'_') state = -1;
            else if (isalnum(s[i])) state = 2;
		    else state = -1;
		    break;
		case 5:
		    if (isalnum(s[i])) state = 5;
		    else if ((int)s[i] == (int)'.') state = 6;
		    else if ((int)s[i] == (int)'-') state = 6;
		    else if ((int)s[i] == (int)'_') state = 6;		    
		    else state = -1;
		    break;
	    case 6:
	        if (isdigit(s[i])) state = 5;
	        else if (isalpha(s[i])) state = 7;
		    else if ((int)s[i] == (int)'.') state = -1;
		    else if ((int)s[i] == (int)'-') state = -1;
		    else if ((int)s[i] == (int)'_') state = -1;	        
		    else state = -1;
	        break;
	    case 7:
	        if ((int)s[i] == (int)'.') state = 6;
		    else if ((int)s[i] == (int)'-') state = 6;
		    else if ((int)s[i] == (int)'_') state = 6;		    
		    else if (isalpha(s[i])) state = 8;
		    else if (isdigit(s[i])) state = 10;
		    else state = -1;
		    break;
		case 8:
		    if ((int)s[i] == (int)'.') state = 6;
		    else if ((int)s[i] == (int)'-') state = 6;
		    else if ((int)s[i] == (int)'_') state = 6;		    
		    else if (isalpha(s[i])) state = 9;
		    else if (isdigit(s[i])) state = 10;
		    else state = -1;
		    break;
		 case 9:
		    if ((int)s[i] == (int)'.') state = 6;
		    else if ((int)s[i] == (int)'-') state = 6;
		    else if ((int)s[i] == (int)'_') state = 6;		    
		    else if (isalpha(s[i])) state = 10;
		    else if (isdigit(s[i])) state = 10;
		    else state = -1;
		    break;
		case 10:
		    if ((int)s[i] == (int)'.') state = 6;
		    else if ((int)s[i] == (int)'-') state = 6;
		    else if ((int)s[i] == (int)'_') state = 6;		    
		    else if (isalnum(s[i])) state = 10;
		    else state = -1;
		    break;
	    case -1:
	        // fail state
	        state = -1;
	        break;
		}
		if(TRACE)cout << " " << s[i] << " " << state << endl;
	}
	if (state==8 || state == 9)
	    return true;
	else
	    return false;
	//return state==3;  // returns true, if state == 3, else false 
}