c#字符串的学习

字符串的声明和初始

   string str1 = "we are student";
            string str2= "we are student";
            Console.WriteLine(str1);
            Console.WriteLine(str2);
            Console.ReadKey();

---

提取字符串信息

获取字符串长度

string str1 = "123 456";
            int size = str1.Length;
            Console.WriteLine(size);
            Console.ReadKey();

获取指定位置字符

 string str1 = "123 456";
            char str = str1[5];
            Console.WriteLine("索引为5的为{0}",str);
            Console.ReadKey();

获取子字符串索引

string str1 = "123 456";
            int size=str1.IndexOf('4');
            Console.WriteLine("4的索引为{0}",size);
            Console.ReadKey();
//
//最后一次搜索值得索引
            string str1 = "123 4564";
            int size=str1.LastIndexOf('4');
            Console.WriteLine("最后一个4的索引为{0}",size);
            Console.ReadKey();

判断字符串首尾内容

 //首尾内容判断
            string _name = "世界上最好的语言c#";
            bool flag=_name.StartsWith("世界");
            bool flag2 = _name.EndsWith("c#");
            Console.WriteLine(flag);
            Console.WriteLine(flag2);
            Console.ReadKey();

---

字符串操作

拼接字符串

 //拼接字符串
            string str1 = "123";
            string str2 = "456";
            string s=str1+""+str2;
            Console.WriteLine(s);
            Console.ReadKey();

比较字符串

  //比较字符串
            Console.WriteLine("输入用户名");
            string name=Console.ReadLine();
            Console.WriteLine("输入密码");
            string pwd = Console.ReadLine();
            if (name=="xiaotang"&&pwd.Equals("222"))
            {
                Console.WriteLine("true");
            }
            else
            {
                Console.WriteLine("false");
            }
            Console.ReadKey();

字符串大小写转换

 //大小写转换
            string str = "lean C# C#";
            Console.WriteLine(str.ToUpper());//大写
            Console.WriteLine(str.ToLower());//小写
            Console.ReadKey();

格式化字符串

 //格式化符号c/d
            Console.WriteLine(string.Format("货币哦{0:c}", 123));
            Console.WriteLine(string.Format("分格符显示{0:n0}",123000));
            Console.WriteLine("百分号显示{0:p0},{1:p0}",0.01,0.09);
            Console.ReadKey();

截取字符串

 //截取字符串
            string str = "Program.cs";
            string str1 = str.Substring(0, str.IndexOf('.'));
            Console.WriteLine("文件名"+str1);
            string str2=str.Substring(str.IndexOf("."));
            Console.WriteLine(str2);
            Console.ReadKey();

分割字符串

  string str = "c#,java,javascript";
            char[] arr = { ',' };
            string[] str1= str.Split(arr,StringSplitOptions.RemoveEmptyEntries);
            for (int i = 0;i < str1.Length; i++)
            {
                Console.WriteLine(str1[i]);
            }
            Console.ReadKey();

去除空白内容

 //trim()
            string str = "    c#    ";
            string str1=str.Trim();
            Console.WriteLine(str1);
            Console.WriteLine(str);
            Console.ReadKey();

替换字符串

 //替换字符串replace
            string str = "java nice";
            Console.WriteLine(str);
            string str1 = str.Replace('j', '#');
            Console.WriteLine(str1);
            string str2 = str.Replace("java", "c#");
            Console.WriteLine(str2);
            Console.ReadKey();

---

可变字符串

StringBuilder

//stringbulider可变字符序列
            //Append将文本追加到对象末尾
            //AppendFormat自定义的值加到对象末尾
            //Insert将字符串加到对象指定位置
            //Remove从对象中移除指定字符
            //Replace用另一个字符替换对象内字符
            int num = 111;
            StringBuilder arr1 = new StringBuilder("c#最好");
            arr1.Append("nice");
            Console.WriteLine(arr1);//
            arr1.AppendFormat("{0:c0}", num);
            Console.WriteLine(arr1);//
            arr1.Insert(0, "编程");
            Console.WriteLine(arr1);//
            arr1.Remove(5,arr1.Length-5);
            Console.WriteLine(arr1);//
            arr1.Replace("编程", "计算机");
            Console.WriteLine(arr1);//
            Console.ReadKey();

stringBuilder和string的区别

//string每操作一次创建一个新对象,stringBuilder的每次操作是对自身对象进行操作
//当大量对字符串进行操作时，须使用stringBuilder，避免产生过多的对象