C#实现数值千位（三位）分割

/// <summary>
/// 对数字添加”,“号，可以处理负数以及带有小数的情况
/// </summary>
/// <param name="money"></param>
/// <returns></returns>
public string FormatMoney(string money)
{
//处理带有负号情况
int negNumber = money.IndexOf("-");
string prefix = string.Empty;
if (negNumber != -1)
{
prefix = "-";
money = money.Substring(1);
}
//处理有小数位情况
int decNumber = money.IndexOf(".");
string postfix = string.Empty;
if (decNumber != -1)
{
postfix = money.Substring(decNumber);
money = money.Substring(0, decNumber);
}
//开始添加”,“号
if (money.Length > 3)
{
string str1 = money.Substring(0, money.Length - 3);
string str2 = money.Substring(money.Length - 3, 3);
if (str1.Length > 3)
{
return prefix + FormatMoney(str1) + "," + str2 + postfix;
}
else
{
return prefix + str1 + "," + str2 + postfix;
}
}
else
{
return prefix + money + postfix;
}
}