字符串附加罗马数字

im阅读问题解决问题，不了解以下内容：

• 在第27行中，似乎比迹象大于倒退，但是当我将它们更改为我认为它们应该是程序确实运行的东西时。请让我知道为什么＆lt;>符号是？

• 在第47行开始的字符串函数中，它如何知道要选择哪个字符串？考虑到我在1930年输入，对于900年，该程序以某种方式知道如何超过9个逗号来选择下一个字符串，即" CM"，并且同样30，它也知道它需要超过3个逗号并选择" xxx"。..但是我不确定吗？请让我知道它如何知道选择" CM"＆amp;" xxx"使用我的1930年示例。

#include <iostream>
#include <string>
using namespace std;

//function prototype
string toRomanLiterals(int);
int main()
//program displays Arabic Years as Roman Years
{
//declare integer as number
int integernumber;
//declare a character
char choice;
//do while loop to continue by y or no
do
{
   //do while loop to read integer from user
   //read integer number between 1 and 3000 only
   do
   {
       cout << "Enter a number between 1000 and 3000: ";
       cin >> integernumber;
   }
   while (integernumber < 1000 || integernumber > 3000);
   if (integernumber > 1000 || integernumber < 3000)
   {
       //calling toRomanLiterals function
       string output= toRomanLiterals(integernumber);
       cout << output<<endl;
   }
   //continue to ask until user wishes to stop
   cout << "Would you like to continue? [y/n]" << endl;
   cin >> choice;
}
while (choice != 'n');
return 0;
}
//string toRomanLitrals takes the integer number and converts to a given
//number to a Roman number if it is between 1000 and 3000
string toRomanLiterals(int number)
{
string roman;
int th,h,t,o;
//string array for numbers 1 to 9
string ones[] =
{"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
//string array for numbers 10 to 90
string tens[] =
{"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
//string array for numbers 100 to 900
string hundreds[] =
{"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
//string array for numbers 1000 to 3000
string thousands[] = {"", "M", "MM", "MMM"};
if (number <= 3000)
{
    //get number of thousands
    th = number/1000;
    number = number % 1000;
    //get number of hundreds
    h = number/100;
    number = number % 100;
    //get number of tens
    t = number/10;
    o = number % 10;
    //concatenate all string values of thousands, hundreds, tens, zeros
    //concatenate all symbols
    roman += thousands[th].append(hundreds[h])
            .append(tens[t]).append(ones[o]);
}
return roman;
}