状态机学习（一）统计字符

题目来自<系统程序员成长计划>

作者:李先静.

逐个字符扫描根据是否为字母决定当前状态由单词内状态切换到单词外计数字符加1

#include <iostream>
#include <string>
#include <vector>
 
using namespace std;
 
string testString = " this's a test,'Hello World!!!' Welcome to the real world, it sucks, but you are gona love it!!!";
 
enum STATE {
    STAT_INIT,
    STAT_IN_WORD,
    STAT_OUT_WORD
};
 
size_t CountWords(const string& s)
{
    int count = 0;
    STATE state = STAT_INIT;
    for (size_t i = 0; i < s.size(); i++)
    {
        switch (state)
        {
        case STAT_INIT:
            if (isalpha(s[i])) {
                state = STAT_IN_WORD;
            }else
            {
                state = STAT_OUT_WORD;
            }
            break;
        case STAT_IN_WORD:
            if (isalpha(s[i])) {
                state = STAT_IN_WORD;
            }
            else {
                count++;
                state = STAT_OUT_WORD;
            }
            break;
        case STAT_OUT_WORD:
            if (isalpha(s[i])) {
                state = STAT_IN_WORD;
            }
            else {
                state = STAT_OUT_WORD;
            }
            break;
        default:
            break;
        }//switch (state)
    }
    if (STAT_IN_WORD == state) {
        count++;
    }
     
    return count;
}
 
int main()
{
    cout << CountWords(testString) << endl;
 
 
       return 0;
}

　　改进版计数以外还讲单词放入容器

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#include <iostream>
#include <string>
#include <vector>
 
using namespace std;
 
string testString = " this's a test,'Hello World!!!' Welcome to the real world, it sucks, but you are gona love it!!!";
 
enum STATE {
    STAT_INIT,
    STAT_IN_WORD,
    STAT_OUT_WORD
};
 
size_t CountWords(const string& s)
{
    int count = 0;
    STATE state = STAT_INIT;
    for (size_t i = 0; i < s.size(); i++)
    {
        switch (state)
        {
        case STAT_INIT:
            if (isalpha(s[i])) {
                state = STAT_IN_WORD;
            }else
            {
                state = STAT_OUT_WORD;
            }
            break;
        case STAT_IN_WORD:
            if (isalpha(s[i])) {
                state = STAT_IN_WORD;
            }
            else {
                count++;
                state = STAT_OUT_WORD;
            }
            break;
        case STAT_OUT_WORD:
            if (isalpha(s[i])) {
                state = STAT_IN_WORD;
            }
            else {
                state = STAT_OUT_WORD;
            }
            break;
        default:
            break;
        }//switch (state)
    }
    if (STAT_IN_WORD == state) {
        count++;
    }
     
    return count;
}
 
size_t word_segmentation(const string& s, vector<string>& strVec)
{
    STATE state = STAT_INIT;
    size_t count = 0;
    size_t subStrStart = string::npos;
    size_t subStrEnd = string::npos;
 
    for (size_t i = 0; i < s.size(); i++)
    {
        switch (state)
        {
        case STAT_INIT:
            if (isalpha(s[i])) {
                subStrStart = i;
                state = STAT_IN_WORD;
            }
            break;
        case STAT_IN_WORD:
            if (!isalpha(s[i])){
                count++;
                subStrEnd = i;
                strVec.push_back(s.substr(subStrStart, subStrEnd- subStrStart));
                state = STAT_OUT_WORD;
            }
            break;
 
        case STAT_OUT_WORD:
            if (isalpha(s[i])) {
                subStrStart = i;
                state = STAT_IN_WORD;
            }
            break;
        default:
            break;
        }//switch (state)
    }
     
    if (state == STAT_IN_WORD) {
        count++;
        subStrEnd = s.size();
        strVec.push_back(s.substr(subStrStart, subStrEnd- subStrStart));
    }
 
    return count;
}
 
 
int main()
{
    cout << CountWords(testString) << endl;
 
    vector<string> strVec;
    cout << word_segmentation(testString, strVec) << endl;
 
    for (vector<string>::iterator it = strVec.begin();
        it != strVec.end(); it++)
    {
        cout << *it << "  ";
    }
    cout << endl;
 
 
    return 0;
}