String class

== and Equals The difference between

1、 Value type

== and Equals The contents of the comparison are consistent , It's all comparative content

string a = "123";// value

            Console.WriteLine(a=="123");

            Console.WriteLine(a.Equals("123"));

2、 Reference type

           ==：  Compare whether the first address is equal   Equals： The comparison is whether the values are equal

char[] x={ '1','2','3'};

            string b = newstring(x);// quote

            Console.WriteLine(b=="123");

   Console.WriteLine(b.Equals("123"));

1） String comparison

Compare(str1, str2)

str1.CompareTo(str2)

string a = "hello",b="Hello",c="hello";

            Console.WriteLine(a.CompareTo(b));//-1

            Console.WriteLine(string.Compare(a,b));//-1

   Console.WriteLine(a.CompareTo(c));//0

1. String lookup

(1)Contains(Findstr)： Find whether the specified string contains a string Findstr, The return value of bool type , That is, only

true and false.

(2)、IndexOf(Findstr)： lookup FindStr First occurrence in string , The return value is the first occurrence

The subscript , If not found, return -1.

(3)、LastIndexOf(FindStr)： lookup FindStr Last occurrence in string , Return value is last

The subscript of one occurrence , If not found, return -1.

Console.WriteLine(a.Contains("lo"));//true

            Console.WriteLine(a.IndexOf('e'));//1

    Console.WriteLine(a.LastIndexOf('l'));//3

1. String truncation

SubString(StartIndex)： Subscript in string from StartIndex Start all subsequent strings .

SubString(StartIndex, Len)： Subscript in string from StartIndex Start the back Len A string of length .

Console.WriteLine(a.Substring(1));//ello

         Console.WriteLine(a.Substring(1,3));//ell

1. Segmentation of strings

Split(SplitCh)： The string Press SplitCh Segmentation , Its return value is an array of strings .

string d=" Hoe standing grain gradually pawning a midday # Sweat dripping under the grass # Who knows what's on the plate # Every grain is hard ";

            string[] e = d.Split('#');

            for (int i = 0; i < e.Length; i++)

            {

                Console.WriteLine(e[i]);

    }

1. String merging

string.Concat(str1, str2, …., strn)： take n String connection , There is no connector in the middle

“+” Connection symbol

string f = "world";

            Console.WriteLine(a+f);

            Console.WriteLine(1+2+3+a);//6hello

            Console.WriteLine(a+1+2+3);//hello123

   Console.WriteLine(string.Concat(a,f));//helloworld

1. String replacement

Replace(oldStr, newStr)： use newStr To replace... In the string oldStr

Console.WriteLine(a.Replace("he","HE"));//HEllo

1. String insertion

Insert(index, str)：index Is where you need to insert ,str Is the character to insert

Console.WriteLine(a.Insert(1,"ww"));//hwwello

1. Deletion of string

Trim()： Delete the spaces at the beginning and end of the string

Remove(Start)：Start For the starting position to be deleted , The method is to delete all characters after the position
         Remove(Start, Len)：Len It refers to the length to be deleted , Different from the above format, it starts from the starting position

Delete Len Characters

string s = " aaa bbb ccc ";

            Console.WriteLine(s.Trim());//aaa bbb ccc

            Console.WriteLine(s.Remove(6));// aaa b

   Console.WriteLine(s.Remove(2,7));// aaccc

9） String case conversion
                  ToLower()： Convert the string to lowercase
                  ToUpper()： Convert string to uppercase

10）string.Format()

string.Format("{0:d}",System.DateTime.Now) // The result is ：2021-3-23（ The location of the month is not 03）

string.Format("{0:D}",System.DateTime.Now) // The result is ：2021 year 3 month 23 Japan

string.Format("{0:f}",System.DateTime.Now) // The result is ：2021 year 3 month 23 Japan 15:37

string.Format("{0:F}",System.DateTime.Now) // The result is ：2021 year 3 month 23 Japan 15:37:52

string.Format("{0:g}",System.DateTime.Now) // The result is ：2021-3-23 15:38

string.Format("{0:G}",System.DateTime.Now) // The result is ：2021-3-23 15:39:27

string.Format("{0:m}",System.DateTime.Now) // The result is ：3 month 23 Japan

string.Format("{0:t}",System.DateTime.Now) // The result is ：15:41

string.Format("{0:T}",System.DateTime.Now) // The result is ：15:41:50