string.cpp，RUN

#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <map>
#include <cstring>

//////////////////////////////////////////////////////////////////////////////////////////////////
//输入数值和字符(不带空格)
void InputNumberAndChar()
{
	//year-month-day
	int year, month, day;
	char temp1, temp2;
	while (std::cin >> year >> temp1 >> month >> temp2 >> day)
	{//Ctrl+Break will break the loop
		std::cout << year << temp1 << month << temp2 << day << std::endl;
	}
}

//输入带空格的字符串
void InputStringWithBlanks()
{
	//http://www.cplusplus.com/reference/string/string/getline/
	std::string str;
	std::getline(std::cin, str); //std::getline(std::cin, str, '\n');遇到'\n停止读入数据

	char temp[256];
	std::cin.getline(temp, sizeof(temp));
}

//////////////////////////////////////////////////////////////////////////////////////////////////

//基本的字符串用法
void BasicStringFunction()
{
	//convert char array to string
	char cMsg[] = "Hello world.";
	std::string str(cMsg); 

	//convert a number to a string
	int n = 10;
	str = std::to_string(n); 

	//convert a string to a number
	int m = std::stoi(str); 

	str = str + " add"; //operator +
	if (str == "str")
	{//operator compare

	}

	char temp[256];
	strcpy_s(temp, str.c_str()); //convert a string to a char array
	std::cout << temp << std::endl;

	{//从字符串中输入
		std::string content = "ABS 10 12.3";
		std::stringstream ss(content);
		std::string v0;
		int v1;
		float v2;
		ss >> v0 >> v1 >> v2;
		std::cout << v0 << "\t" << v1 << "\t" << v2 << std::endl;
	}
}

//http://www.cplusplus.com/reference/string/string/find/
//查找指定的字符串str(完全包含)
int PatternNumber(const std::string& content, const std::string& str)
{
	int count = 0;
	size_t pos = content.find(str);
	while (pos != std::string::npos)
	{
		count++;
		pos = content.find(str, pos + 1);
	}
	return count;
}

//http://www.cplusplus.com/reference/string/string/find_first_of/
//查找字符串中，包含模式str的次数（出现str包含的任一字符）
int PatternNumber_OneOf(const std::string& content, const std::string& str)
{
	int count = 0;
	size_t pos = content.find_first_of(str);
	while (pos != std::string::npos)
	{
		count++;
		pos = content.find_first_of(str, pos + 1);
	}
	return count;
}

//把输入content里的符号换成空格
void ReplaceSymbolWithBlank(std::string& content)
{
	//http://www.cplusplus.com/reference/string/string/find_first_of/
	const std::string Pattern = ".,\"!?-"; //句子中使用的符号
	std::size_t found = content.find_first_of(Pattern);
	while (found != std::string::npos)
	{
		content[found] = ' ';
		found = content.find_first_of(Pattern, found + 1);
	}
}

//利用std::stringstream统计句子中单词个数，单词之间用 空格 \t \n 分离
//输入字符串不包含无关的符号，如.,"?!等
void ParseContent(const std::string& content, std::vector<std::string>& vWords)
{
	std::stringstream ss(content);
	std::string word;
	while (ss >> word) //标准的流输入
	{
		vWords.push_back(word);
	}
}

//https://en.cppreference.com/w/cpp/container/map
//统计词频
//输入：vWords，输出：msu，map映射
void WordFrequency(const std::vector<std::string>& vWords, std::map<std::string, unsigned int>& msu)
{
	for (auto i = 0; i < vWords.size(); i++)
	{
		//https://en.cppreference.com/w/cpp/container/map/find
		//在msu中查找key为vWords[i]的项
		if (msu.find(vWords[i]) == msu.end())//msu中没有word
		{	//不存在，添加一项
			//https://en.cppreference.com/w/cpp/container/map/operator_at
			msu[vWords[i]] = 1;
		}
		else
		{	//找到，直接使用
			//https://en.cppreference.com/w/cpp/container/map/operator_at
			msu[vWords[i]]++;
		}
	}
}

//显示词频信息
void Show(const std::map<std::string, unsigned int>& msu)
{
	//访问std::map结构
	//https://en.cppreference.com/w/cpp/container/map/begin
	for (auto itr = msu.begin(); itr != msu.end(); itr++)
	{
		std::cout << itr->first << ": " << itr->second << std::endl;
	}
}

//提取句子中包含的单词，以及其它信息
void ParseContent(const std::string& content)
{
	std::string temp = content;
	ReplaceSymbolWithBlank(temp); //把temp中的.,"?!等符号替换成空格

	std::vector<std::string> vWords;
	ParseContent(temp, vWords); //根据空格分割信息提取单词

	//std::map结构可以用来存储词频
	//https://en.cppreference.com/w/cpp/container/map
	std::map<std::string, unsigned int> msu;
	WordFrequency(vWords, msu);

	Show(msu); //显示词频信息

	auto nWords = vWords.size();
	const std::string Pattern = ".,\"!?-"; //字符串处理示例时使用，句子中使用的符号
	auto nSymbols = PatternNumber_OneOf(content, Pattern);//统计包含模式的次数
}

int main()
{
	std::string content1;
	std::string content2;

	content1 = "Although the principles of structured programming improved the clarity, reliability, and ease of maintenance of programs, large - scale programming still remains a challenge.OOP \
		brings a new approach to that challenge.";
	content2 = "Unlike procedural programming, which emphasizes \
		algorithms, OOP emphasizes the data.Rather than try to fit a problem to the procedural \
		approach of a language, OOP attempts to fit the language to the problem.";

	std::string content = content1 + content2;
	ParseContent(content);

	//InputNumberAndChar();
	//InputStringWithBlanks();
	BasicStringFunction();

	return 0;
}