refactor: Add String example code in basic_part1.

lib/basic_part1.dart

@@ -39,6 +39,32 @@ void basic_build_in_types() {
   print("hitPoints <= 0? ${hitPoints <= 0}");
 
 
+  print("\nDart Strings:");
+  String str1 = "It's a string with double quotes";
+  String str2 = 'It\'s a string with single quote';
+  String str3 = """
+  It's a long string with triple double quotes
+  這是一個很長的字串
+  """;
+  print(str1);
+  print(str2);
+  print(str3);
+
+  const aConstNum = 0;
+  const aConstBool = true;
+  const aConstString = 'a constant string';
+
+  var aNum = 0;
+  var aBool = true;
+  var aString = 'a string';
+  const aConstList = [1, 2, 3];
+
+  const validConstString = '$aConstNum $aConstBool $aConstString';
+  // const invalidConstString = '$aNum $aBool $aString $aConstList';
+  print("validConstString: $validConstString");
+  print("$aNum $aBool $aString $aConstList, ${aConstList[0]}");
+
+
   print("\nDart List:");
   // List & Generics(泛型)
   List<String> fruits = ['bananas', 'grapes', 'oranges'];