FSM_Basic

#include <stdio.h>

enum states { before = 0, inside = 1, after = 2 };

class StateMachine
{
  private:
    enum states state;                                      // Current state
    struct branch
    {
        enum states new_state:2;
        int should_putchar:1;
    };
    static struct branch transition_table[3][3];           // Transition map

public:
    StateMachine() : state(before) {}                      // Constructor with starting state
    void process_event(int c)
    {
        int idx2 = (c == ' ') ? 0 : (c == '\n') ? 1 : 2;
        struct branch *b = & transition_table[state][idx2];
        state = b->new_state;
        if(b->should_putchar) putchar(c);
    }
};

struct StateMachine::branch StateMachine::transition_table[3][3] =
{
                 /* ' '         '\n'        others */
    /* before */ { {before,0}, {before,1}, {inside,1} },
    /* inside */ { {after, 0}, {before,1}, {inside,1} },
    /* after  */ { {after, 0}, {before,1}, {after, 0} }
};

int main(void)
{
    int c;
    StateMachine FSM;
    while((c = getchar()) != EOF)
        FSM.process_event(c);
    return 0;
}