Finite State Machine Project Help

**ryanbradley** · 03-06-2004

I am currently taking a class in C++ which has been going very well until our current assignment. The asignment is to build a finite state machine that will take in inputs from the user see whether it is an identifier or a digit and the transistion to an approriate stage to deal with those. For example someone inputs: R2D2,Time,48,2,rate,555666. would output

R2D2 -identifier
Time -identfier
48 -number
2 -number
and so on until it reaches the end. The program is supposed to parse each character to see what it is and from there transition to a different state. If it starts as a digit it goes from start state to digit state where it checks for more digits until it reads a comma which then says its done and it s a number so it transitions to the number state which saves it as a number and then transistions back to start. If it is a character then it goes to the build identfier state which looks for a letter or didgit to make up the name and the once again a , will terminate it and call it to the identifier state which then goes back to start. This parsing repeats until a period is found which ends the program.

A little more background information is that why are in a chapter dealing with functions so I am assuming a vast majority of this will be functions. I was informed by the professor using isalpha and isdigit will be crucial but he gave no information on there implementation and I can't find a source that explains them in a way I understand, he also said to use a case switchblock. So my idea was once I get the isalpha is digit figured out I could put those in a case switch block and when it finds if its a char or digit it goes to the approaiate state. As far as the states are concerned I was going to make each one a function and when it tansitioned just have it call the next function.

Sorry for the super long post buyt I am completly lost and can use any help anybody can offer. Thanks for taking the time to read this and any input is greatly appreciated.

Ryan Bradley

**/Muad'Dib\** · 03-06-2004

If your using strings, you could iterate through the string and us isalpha, isalnum, isdigit etc. If your using char or char*, try using pointer arithmetic to move along the string, and parse the input. Since the commas specify the begining of a new type in your input (identifier, number etc) when you reach one of them via pointer or iterator ignore it and make sure the program knows that a new word must be recognized. Add the results either into an array or vector, and then output them at the end of the program.

**ryanbradley** · 03-06-2004

The only problem is we have not yet covered vectors, arrays or pointers and as such am unable to use them. I am basically able to work with simple user created functions, loops and other very basic C++ features.
Thanks,
Ryan Bradley

**Salem** · 03-06-2004

Read this

You need to draw a state transition diagram, with I guess these states
- initial (you start here)
- identifier
- number
- comma
- terminal (you finish here)

In each instance, you
- look at your current state
- look at the next character
to determine what your new state should be.

When you change state, you output the sequence of symbols you accumulated in the old state.

> I was informed by the professor using isalpha and isdigit will be crucial but he gave no information on there implementation
They're prototyped in ctype.h (or just ctype for C++ users)
You use them like
if ( isalpha('a') )

**/Muad'Dib\** · 03-06-2004

Code:

#include <iostream>

int main()
{

	char input[20]; //the buffer should be larger
	std::cout << "Enter input: ";
	std::cin >> input;

	int count = 0;

	for(int i = 0; i < strlen(input); i++) //iterate through the string
	{
		if(isalpha(input[i]))
			std::cout << "alpha\n"; 
		if(isdigit(input[i]))
			std::cout << "digit\n";
	}


	return 0;
}

Of course in the if statements you would check for the stuff that Salem just mentioned.

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