替换空格

实现一个函数，将一个字符串中的每个空格替换成"%20"。例如，当字符串为"We Are Happy."，则经过替换之后的字符串为"We%20Are%20Happy."。

using System.Text;

namespace JianZhiOffer
{
    class ReplaceSpace
    {
        public string replaceSpace(string str)
        {
            // write code here
            if (str == null)
            {
                return null;
            }

            StringBuilder strBuff = new StringBuilder();

            for (int i = 0; i < str.Length; i++)
            {
                if (str[i] == ' ')
                {
                    strBuff.Append(@"%20");
                }
                else 
                {
                    strBuff.Append(str[i]);
                }
            }

            return strBuff.ToString();
        }
    }
}