C++【string类操作】递归实现数字转化为英文名称

代码如下：

#include
#include
#include
#include
using namespace std;


class Num2Clause
{
private:
	int num;//待转化数字
	//字符串数组
	static const string onesNames[];//个位数
	static const string tenAboves[];//10-19
	static const string tensNames[];//整十数字
	static const string levelNames[];//数量级

public:
	//构造函数
	Num2Clause(int num)
	{
		this->num = num;
	}
	//仅处理两位非负数：
	string toString2D()
	{
		if (num < 10)
			return onesNames[num];
		else if (num < 20)
			return tenAboves[num - 10];
		else if (num % 10 == 0)
			return tensNames[num / 10];
		else
			//字符串拼接 (递归法)
			return tensNames[num / 10] + " " + (new Num2Clause(num % 10))->toString2D();
			//或者用加法：
		//	return tensNames[num / 10] + " " + onesNames[num % 10];
	}
	//仅处理三位非负数：
	string toString3D()
	{
		if (num < 100)
			return toString2D();
		else if (num % 100 == 0)
			return onesNames[num / 100] + " " + levelNames[0];
		else
			return onesNames[num / 100] + " " + levelNames[0] + " and " + (new Num2Clause(num % 100))->toString3D();
	}
	//处理 2147483647 以内的实数
	string toString()//toString中可调用toString2D ,但可能需做修改
	{
		int len = to_string(num).length();//数字位数
		int lev = (len - 1) / 3;//数字等级
		//是否为负数
		if (num < 0)
			return "minus " + (new Num2Clause(-num))->toString();
		else
		{
			if (lev == 0)
				return toString3D();
			else if (num % (int)pow(1000, lev) == 0)
				return (new Num2Clause(num / (int)pow(1000, lev)))->toString() + " " + levelNames[lev];
			else
				return (new Num2Clause(num / (int)pow(1000, lev)))->toString() + " " + levelNames[lev]
						+ " "+ (new Num2Clause(num % (int)pow(1000, lev)))->toString();
		}
	}

	static void plainTest()
	{
		//简单class测试函数
		for (int n = 0; n < 100; n += 3)
		{
			cout << setw(5) << n << " => "" << (new Num2Clause(n))->toString() << """ << endl;
		}
	}

	static void interactiveTest(int n = 7)
	{
		//交互式测试
		cout << (new  Num2Clause(n))->toString() << endl;
		cout << " Input New Number Here : ";
		cin >> n;
		return interactiveTest(n);
	}
};

const string Num2Clause::onesNames[] = { "zero" , "one" , "two" ,"three" , "four",
										 "five" , "six" , "seven" , "eight" , "nine" , "ten" };
const string Num2Clause::tenAboves[] = { "ten" , "eleven" , "twelve" , "thirteen" , "fourteen",
										 "fifteen" , "sixteen" , "seventeen" , "eighteen" , "nineteen" };
const string Num2Clause::tensNames[] = { "zero" , "ten" , "twenty" , "thirty" , "forty",
										 "fifty" , "sixty" , "seventy" , "eighty" , "ninety" };
const string Num2Clause::levelNames[] = { "hundred","thousand","million","billion","trillion" };

int main()
{
	Num2Clause::plainTest();
	Num2Clause::interactiveTest();
	return 0;
}