State machines are very simple in C if you use function pointers.

statemachine.c

/*
http://stackoverflow.com/questions/1371460/state-machines-tutorials/1371654#1371654

State machines are very simple in C if you use function pointers.

Basically you need 2 arrays - one for state function pointers and one for state 
transition rules. Every state function returns the code, you lookup state 
transition table by state and return code to find the next state and then 
just execute it.
*/

int entry_state(void);
int foo_state(void);
int bar_state(void);
int exit_state(void);

/* array and enum below must be in sync! */
int (* state)(void)[] = { entry_state, foo_state, bar_state, exit_state};
enum state_codes { entry, foo, bar, end};

enum ret_codes { ok, fail, repeat};
struct transition {
    enum state_codes src_state;
    enum ret_codes   ret_code;
    enum state_codes dst_state;
};
/* transitions from end state aren't needed */
struct transition state_transitions[] = {
    {entry, ok,     foo},
    {entry, fail,   end},
    {foo,   ok,     bar},
    {foo,   fail,   end},
    {foo,   repeat, foo},
    {bar,   ok,     end},
    {bar,   fail,   end},
    {bar,   repeat, foo}};

#define EXIT_STATE end
#define ENTRY_STATE entry

int main(int argc, char *argv[]) {
    enum state_codes cur_state = ENTRY_STATE;
    enum ret_codes rc;
    int (* state_fun)(void);

    for (;;) {
        state_fun = state[cur_state];
        rc = state_fun();
        if (EXIT_STATE == cur_state)
            break;
        cur_state = lookup_transitions(cur_state, rc);
    }

    return EXIT_SUCCESS;
}

/*
I don't put lookup_transition() function as it is trivial.

That's the way I do state machines for years.
*/