根据字符串截取想要的位置加标识或者换行，指定规则每多少个字后添加换行

public string TransWantText(string sequence, int howMany = 100, int howLine = 5, string lineCode = "<br />")
{
    //5行
    //ToUpper()

    string resultStr = string.Empty;

    //转换为大写
    string sourceStr = sequence.ToUpper();

    int length = sourceStr.Length;

    int maxLine = length / howMany > howLine ? howLine : Convert.ToInt32(length / howMany);

    //循环N次
    for (int i = 0; i < maxLine; i++)
    {
        resultStr += sourceStr.Substring(howMany * i, howMany) + lineCode;
    }

    return resultStr;

}

.NET 字符串指定规则添加换行