C# 字符串属性

using System;
public class Demo {
   public static void Main() {
      string str1 = "h8b9";
      string str2 = "abcdef";
      Console.WriteLine("Is string1 null or empty? = "+string.IsNullOrEmpty(str1));
      Console.WriteLine("Is string2 null or empty? = "+string.IsNullOrEmpty(str2));
      bool val = str1 != str2;
      Console.WriteLine("Is str1 equal to str2? = "+val);
      for (int i = 0; i < str1.Length; i++) {
         if (Char.IsLetter(str1[i]))
            Console.WriteLine(""+str1[i]+" is a letter");
         else
            Console.WriteLine(""+str1[i]+" is a number");
      }
   }
}

Is string1 null or empty? = False
Is string2 null or empty? = False
Is str1 equal to str2? = True
h is a letter
8 is a number
b is a letter
9 is a number

using System;
public class Demo {
   public static void Main() {
      string str1 = "hijklm";
      string str2 = String.Empty;
      Console.WriteLine("Is string1 null or whitespace? = "+String.IsNullOrWhiteSpace(str1));
      Console.WriteLine("Is string2 null or whitespace? = "+String.IsNullOrWhiteSpace(str2));
      Console.WriteLine("String1 length = "+str1.Length);
      Console.WriteLine("String2 length = "+str1.Length);
      Console.WriteLine("String length = "+"demo".Length);
   }
}

Is string1 null or whitespace? = False
Is string2 null or whitespace? = True
String1 length = 6
String2 length = 6
String length = 4