一个简单的有穷状态机-单词数统计程序

#include <iostream>
#include <cctype>

class WordCounter
{
    enum class _state
    {
        STATE_INIT = 0,
        STATE_IN_WORD,
        STATE_OUT_WORD,
    };
public:
    static int count_words(const char* text);
};

int WordCounter::count_words(const char* text)
{
    int counts = 0;
    _state state = _state::STATE_INIT;
    const char* it = text;

    for (; *it != '\0'; it++)
    {
        switch (state)
        {
        case WordCounter::_state::STATE_INIT:
            if (isalpha(*it))
            {
                state = _state::STATE_IN_WORD;
            }
            else
            {
                state = _state::STATE_OUT_WORD;
            }
            break;
        case WordCounter::_state::STATE_IN_WORD:
            if (!isalpha(*it))
            {
                state = _state::STATE_OUT_WORD;
                //状态发生转换
                counts++;
            }
            break;
        case WordCounter::_state::STATE_OUT_WORD:
            if (isalpha(*it))
            {
                state = _state::STATE_IN_WORD;
            }
            break;
        default:
            break;
        }//switch
    }//for
    if (_state::STATE_IN_WORD == state)
    {
        counts++;
    }
    return counts;
}

int main(int argc, const char* argv[])
{
    using namespace std;
    char* text = "   my  name is\r\n Percy!!this is BBC English";
    cout << text << '\n' << WordCounter::count_words(text) << endl;
    getchar();
    return 0;
}

使用状态机的直接好处就是让问题分析简单化。