c#控制台怎样输入密码给字符串加密再输出加密后的字符串

public static string a(string s) { StringBuilder sb = new StringBuilder(); for (int i = 0; i < s.Length; i++) { int t=Convert.ToInt32(s[i]); if (t>= 48 &&t<= 57) { sb.Append('$'); } sb.Append(s[i]); } return sb.ToString();