添加Lesson23

C#核心/C#核心.sln

@@ -53,6 +53,10 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Lesson22_面向对象相关
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Lesson22_面向对象相关-万物之父中的方法练习", "Lesson22_面向对象相关-万物之父中的方法练习\Lesson22_面向对象相关-万物之父中的方法练习.csproj", "{0AF0A54F-67BE-46A2-B79D-813ACB6A9EF3}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Lesson23_面向对象相关-String", "Lesson23_面向对象相关-String\Lesson23_面向对象相关-String.csproj", "{24664BCD-DCDC-4DFC-B597-E22D98C3A206}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Lesson23_面向对象相关-String练习", "Lesson23_面向对象相关-String练习\Lesson23_面向对象相关-String练习.csproj", "{E35D8933-50D7-496A-8E4C-06DDD1CC0878}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -159,6 +163,14 @@ Global
 		{0AF0A54F-67BE-46A2-B79D-813ACB6A9EF3}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{0AF0A54F-67BE-46A2-B79D-813ACB6A9EF3}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{0AF0A54F-67BE-46A2-B79D-813ACB6A9EF3}.Release|Any CPU.Build.0 = Release|Any CPU
+		{24664BCD-DCDC-4DFC-B597-E22D98C3A206}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{24664BCD-DCDC-4DFC-B597-E22D98C3A206}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{24664BCD-DCDC-4DFC-B597-E22D98C3A206}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{24664BCD-DCDC-4DFC-B597-E22D98C3A206}.Release|Any CPU.Build.0 = Release|Any CPU
+		{E35D8933-50D7-496A-8E4C-06DDD1CC0878}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E35D8933-50D7-496A-8E4C-06DDD1CC0878}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E35D8933-50D7-496A-8E4C-06DDD1CC0878}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{E35D8933-50D7-496A-8E4C-06DDD1CC0878}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

C#核心/Lesson23_面向对象相关-String/Lesson23_面向对象相关-String.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <RootNamespace>Lesson23_面向对象相关_String</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

C#核心/Lesson23_面向对象相关-String/Program.cs

@@ -0,0 +1,96 @@
+namespace Lesson23_面向对象相关_String
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            #region 知识点一 字符串指定位置获取
+            //string是一个密封类，不能被继承
+            //字符串的本质是一个char数组
+            string str = "123";
+            Console.WriteLine(str[0]);//一个类能通过中括号访问，那么这个类就实现了索引器
+
+            //转换为char数组
+            char[] chars = str.ToCharArray();
+            Console.WriteLine(chars[1]);
+            for (int i = 0; i < chars.Length; i++)
+            {
+                Console.Write(chars[i]);
+            }
+            Console.WriteLine();
+            #endregion
+
+            #region 知识点二 字符串拼接
+            str = string.Format("{0},{1}", 1, 2);
+            Console.WriteLine(str);
+            str = "123" + "456";
+            Console.WriteLine(str);
+            Console.WriteLine();
+            #endregion
+
+            #region 知识点三 正向查找字符位置
+            str = "abcdefg";
+            int index = str.IndexOf("b");
+            Console.WriteLine(index);
+            index = str.IndexOf("noindex");
+            Console.WriteLine(index);//找不到返回-1
+
+            #endregion
+
+            #region 知识点四 反向查找指定字符串位置
+            str = "123321";
+            index = str.IndexOf("2");//正向查找第一个2
+            Console.WriteLine(index);
+            index = str.LastIndexOf("2");
+            Console.WriteLine(index);//反向查找第一个2
+            Console.WriteLine();
+            #endregion
+
+            #region 知识点五 移除指定位置后的字符
+            str = "1234567890";
+            Console.WriteLine(str);
+            str = str.Remove(5);//移除指定位置后的字符
+            Console.WriteLine(str);
+
+            str = str.Remove(1, 3);//从指定位置开始移除指定个数的字符
+                                   //从第1个位置往后移除3个字符
+            Console.WriteLine(str);
+            Console.WriteLine();
+            #endregion
+
+            #region 知识点六 替换指定字符串
+            str = "abcdefg";
+            str = str.Replace("cd", "CD");
+            Console.WriteLine(str);
+            Console.WriteLine();
+            #endregion
+
+            #region 知识点七 大小写转换
+            str = "abcDEF";
+            str = str.ToUpper();
+            Console.WriteLine(str);
+            str = str.ToLower();
+            Console.WriteLine(str);
+            Console.WriteLine();
+            #endregion
+
+            #region 知识点八 字符串截取
+            str = "1234567890";
+            str = str.Substring(3);//从指定位置开始截取到字符串末尾
+            Console.WriteLine(str);
+            str = "1234567890";
+            str = str.Substring(3,5);//从指定位置开始截取指定个数的字符
+            Console.WriteLine(str);
+            #endregion
+
+            #region 知识点九 字符串分割
+            str = "1,2,3,4,5,6";
+            string[] strArray = str.Split(',');//根据指定字符分割字符串，返回字符串数组
+            foreach (var item in strArray)
+            {
+                Console.WriteLine(item);
+            }
+            #endregion
+        }
+    }
+}

C#核心/Lesson23_面向对象相关-String练习/Lesson23_面向对象相关-String练习.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <RootNamespace>Lesson23_面向对象相关_String练习</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

C#核心/Lesson23_面向对象相关-String练习/Program.cs

@@ -0,0 +1,72 @@
+    namespace Lesson23_面向对象相关_String练习
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            Console.WriteLine("string练习题");
+            #region 练习题一
+            //请写出string中提供的截取和替换对应的函数名
+            string str = "123";
+            str = str.Substring(1);
+            str = str.Substring(1, 1);
+
+            str = "123123";
+            str = str.Replace("123", "哈哈哈");
+            #endregion
+
+            #region 练习题二
+            string str1 = "1|2|3|4|5|6|7";
+            string[] strs = str1.Split('|');
+            str1 = "";
+            for (int i = 0; i < strs.Length; i++)
+            {
+                str1 += int.Parse(strs[i]) + 1;
+                if(i < strs.Length - 1)
+                {
+                    str1 += "|";
+                }
+            }
+            Console.WriteLine(str1);
+            #endregion
+
+            #region 练习题四
+            string strr = null;//开了栈内存1，没开堆内存0
+            strr = "123";//堆内存+1
+            string str2 = strr;//栈内存+1
+            str2 = "321";//堆内存+1
+            str2 += "123";//堆内存+1
+                          // 请问，上面这段代码，分配了多少个新的堆空间
+                          //3个
+            #endregion
+
+            #region 练习题五
+            //编写一个函数，将输入的字符串反转。不要使用中间商，你必须原地修改输入数组。交换过程中不使用额外空间
+            //比如：输入{'h','e','l','l','o'}
+            //输出    {'o','l','l','e','h'}
+
+            Console.WriteLine("请输入内容");
+            string str3 = Console.ReadLine();
+            char[] chars = str3.ToCharArray();
+            for (int i = 0; i < chars.Length / 2; i++)
+            {
+                //交换
+                //char temp = chars[i];
+                //chars[i] = chars[chars.Length - 1 - i];
+                //chars[chars.Length - 1 - i] = temp;
+                chars[i] = (char)(chars[i] + chars[chars.Length - 1 - i]);
+                chars[chars.Length - 1 - i] = (char)(chars[i] - chars[chars.Length - 1 - i]);
+                chars[i] = (char)(chars[i] - chars[chars.Length - 1 - i]);
+            }
+
+            for (int i = 0; i < chars.Length; i++)
+            {
+                Console.Write(chars[i]);
+            }
+
+            str3 = new string(chars);
+            Console.WriteLine(str3);
+            #endregion
+        }
+    }
+}