I prefer using function pointers over gigantic switch statements, but in contrast to qrdl's answer I normally don't use explicit return codes or transition tables.
Also, in most cases you'll want a mechanism to pass along additional data. Here's an example state machine:
#include <stdio.h>
struct state;
typedef void state_fn(struct state *);
struct state
{
state_fn * next;
int i; // data
};
state_fn foo, bar;
void foo(struct state * state)
{
printf("%s %i\n", __func__, ++state->i);
state->next = bar;
}
void bar(struct state * state)
{
printf("%s %i\n", __func__, ++state->i);
state->next = state->i < 10 ? foo : 0;
}
int main(void)
{
struct state state = { foo, 0 };
while(state.next) state.next(&state);
}