Thread: Finite State Machine for numbers and identifiers(Wrong output)

First, you should initialize current_state to some appropriate value, otherwise it could end up being any one of your enums at the beginning (altho it is probably none of them).

The reason "rate" is reported as an identifier is because in transition() you have a switch statement for isalpha whose default is current_state = identifier. Since 'r' is not in the switch, that default is used.

Originally Posted by paranoidgnu

I think, you misunderstood my question.I'm asking how output for R2D2 will be Identifier.My program says it's a number

Yes, sorry.

Anyway, you can see the reason. The solution is to take into account the fact that an identifier contains alphabetic characters and can include numeric characters, while a number includes only numeric characters. Also, you only have these two states. So:

Code:

		do{
		scanf("%c", &transition_char[i]);
		i++;
		current_state = transition(current_state, transition_char[i-1]);		
		printf("%c",transition_char[i-1]);
		}while(transition_char[i-1] != ' ' && transition_char[i-1] != '.');

Add a state_t variable here to set the state for a whole word/item. This is by default "number", but if current state comes back as an identifier, you set this state to identifier:

Code:

	state_t tag = start;
          
       [...]
		tag = number; 
		do{
		scanf("%c", &transition_char[i]);
		i++;
		current_state = transition(current_state, transition_char[i-1]);
		if (current_state == identifier) tag = identifier;
		printf("%c",transition_char[i-1]);
		}while(transition_char[i-1] != ' ' && transition_char[i-1] != '.');

Now you have to adjust the rest of the code to deal with this:

Code:

	printf("Enter text> ");
	do{
		if (tag == identifier){
			printf(" - Identifier\n");
			current_state = start;
			tag = number;
		}
		else if (tag == number){
			printf(" - Number\n");
			current_state = start;
		}
		tag = number;

Tested, works, and you should be able to follow the logic.

O_o

I'm sorry, but the reason this is happening is obvious.

There is simply no state machinery in place here. (You are indiscriminately performing the same operations regardless of the current state.) Without that machinery in place, the resulting datum will always pretend to be whatever the last character processed is pretending to be.

In other words, "R2D2" is a number because "2" is a number.

Here is some code to get you started in the right direction. It is needlessly verbose because I simply modified your code. You'll see that I perform different tests with different results depending on the state.

Also, the code is untested as I only typed it into my browser. (My own machines are not available at the moment.)

[Edit]
Oh, and the code builds on what MK27 has said.

If it does work, it is all me; if it doesn't work, blame him. ^_^
[/Edit]

Soma

Code:

#include <stdio.h>
#include <ctype.h>
typedef enum
	{start, building_id, building_num, breaker, stop}
state_t;
typedef enum
	{unknown, number, identifier}
types_t;
state_t transition(state_t current_state, types_t * result_type, char transition_char);
int main(void)
{
	int i = 0;
	state_t current_state;
	types_t result_type;
	char transition_char[30];
	current_state = start;
	result_type = unknown;
	printf("Enter text> ");
	do{
		if (result_type == identifier){
			printf(" - Identifier\n");
			current_state = start;
			result_type = unknown;
		}
		else if ( result_type == number){
			printf(" - Number\n");
			current_state = start;
			result_type = unknown;
		}
		do{
		if(EOF == scanf("%c", &transition_char[i]))
		{
            current_state = stop;
		}
		current_state = transition(current_state, &result_type, transition_char[i]);
		printf("%c", transition_char[i]);
		i++;
		}while(!(current_state == breaker || current_state == stop));
	}while(current_state != stop);

	return(0);
}

state_t transition(state_t current_state, types_t * result_type,char transition_char){
        if(start == current_state)
        {
            if(isdigit((int)transition_char))
            {
                current_state = building_num;
                *result_type = number;
            }
            else if(isalpha((int)transition_char))
            {
                current_state = building_id;
                *result_type = identifier;
            }
            else if (transition_char == ' ')
                current_state = breaker;
            else if (transition_char == '.')
                current_state = stop;
        }
        else if((stop == current_state) || (breaker == current_state))
        {
        }
        else if(building_num == current_state)
        {
            if(isdigit((int)transition_char))
            {
                current_state = building_num;
                *result_type = number;
            }
            else if (transition_char == ' ')
                current_state = breaker;
            else if (transition_char == '.')
                current_state = stop;
        }
        else if(building_id == current_state)
        {
            if (transition_char == ' ')
                current_state = breaker;
            else if (transition_char == '.')
                current_state = stop;
        }
	return(current_state);
}

Originally Posted by paranoidgnu

Nothing changed here,

You missed a couple of crucial bits, and you completely missed the point:

Code:

		do{
		scanf("%c", &transition_char[i]);
		i++;
		current_state = transition(current_state, transition_char[i-1]);
		if (current_state == identifier) 
			tag = identifier;
		else if(current_state == number)
			tag = number;
		printf("%c",transition_char[i-1]);
		}while(transition_char[i-1] != ' ' && transition_char[i-1] != '.');

That just reproduces your original mistake.

The idea is simple: an "identifier" has letters, and possibly numbers. A "number" only has numbers. So if during that do..while, current_state comes back as "identifier", the tag state for that tag/word/item is identifier. Period. End of story. So (and you missed this bit, but it is in the code from my previous post) you set the tag state to "number" before the do..while:

Code:

		tag = number;
		do{

Now, you go thru the loop and if you find alphabetic characters, set tag to "identifier":

Code:

		do{
			scanf("%c", &transition_char[i]);
			i++;
			current_state = transition(current_state, transition_char[i-1]);
			if (current_state == identifier) tag = identifier;
			printf("%c",transition_char[i-1]);
		} while (transition_char[i-1] != ' ' && transition_char[i-1] != '.');

Notice, I DID NOT EXPLICITLY SET TAG TO "NUMBER" INSIDE THIS LOOP. Tag is already "number"; if it changes to "identifier", IT SHOULD REMAIN THAT WAY AND NOT BE CHANGED BACK TO "NUMBER".

The reason I haven't posted the whole program is because: 1) actually it is all here, but in seperate bits, 2) I think it is important for you to think about the changes and the logic behind them. But if you are desperate, ask And it does work, here's the output:

Code:

[root~/C] echo "rate R2D2 48 2 time 555666 ." | ./a.out
Enter text> rate  - Identifier
R2D2  - Identifier
48  - Number
2  - Number
time  - Identifier
555666  - Number