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C (I) C basic grammar all in one
2022-06-11 05:10:00 【Aaaaan】
C# It's from Microsoft （Microsoft） Developed , be based on C and C++ An object-oriented programming language , Its grammatical rules are very similar to Java, Commonly used for rapid development Windows Desktop application . This article will C# Some basic grammar knowledge for quick learning , Quick start .
One .C# Program structure
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace netBasic_learning
{
// The definition of a class
class Rectangle
{
//（1） attribute
double length;
double width;
//（2） Method
public void Acceptdetails()
{
this.length = 4.5;
this.width = 2;
}
public double getArea()
{
return this.length * this.width;
}
public void Display()
{
Console.WriteLine("Length: {0}", length);
Console.WriteLine("Width: {0}", width);
Console.WriteLine("Area: {0}", getArea());
}
//Main Function is the main entry of the program
public static void Main(string[] args)
{
Rectangle rectangle = new Rectangle();
rectangle.Acceptdetails();
rectangle.Display();
// Blocking windows
Console.ReadLine();
}
}
}
1.using Use ：
（1） meaning ： using namespace std , Be similar to Java Of Import
（2） Be careful ：using Keyword is used to include the namespace... In the program . A program can contain more than one using sentence .2.namespace Use ：
（1）namespace Declare the namespace of this class as netBasic_learning, Other places can go through using netBasic_learning To use the classes and methods here
（2） One namespace Can contain multiple classes3.Main Function blocking ：
（1）Console.ReadLine() : The last line Console.ReadLine(); Is aimed at VS.NET User . This causes the program to wait for a carriage return , Prevent the program from Visual Studio .NET On startup, the screen will run quickly and close . That is to prevent the black window from flashing , Block up . meanwhile ReadLine() Method can also be used to read program input . （2）Console.ReadKey() : Its function is the same as above .
4. summary ：
1.C# Grammar basic and Java almost , Both are object-oriented languages . It's just C# Mainly for desktop application development ,Java Main orientation Web application development
2.C# And Java The difference is , The filename can be different from the name of the class .
Two .C# Data types and variables
1. Basic data type
namespace netBasic_learning
{
class Basic_dataType
{
public static void Main(String[] args)
{
//1. Basic data type ： Allocate storage space , Storing data
int Int_number = 1;
double Double_number = 3.14;
bool Bool_number = true;
Console.WriteLine("Int: {0},Double: {1},Bool: {2}", Int_number,Double_number,Bool_number);// Word wrap
}
}
}
2. Reference type
The reference type does not contain the actual data stored in the variable , But they contain references to variables . let me put it another way , They refer to a memory location . When using multiple variables , Reference types can point to a memory location . If the data of the memory location is changed by a variable , Other variables will automatically reflect the change of this value . Built in There are ：object、string And our custom classes Class.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace netBasic_learning
{
class Basic_dataType
{
public static void Main(String[] args)
{
// Reference data type ： The reference address where the data is stored , Another name (Object、String、class)
String str = "Hello World！";
String str_origin = "Hello\nWorld!";// Escape character
String str_change = @"Hello\nWorld!";// Original output @ = "\\"
Console.WriteLine("String str: {0}", str);
Console.WriteLine("String str_origin: {0}", str_origin);
Console.WriteLine("String str_change: {0}", str_change);
}
}
}
3. Data type conversion
One . Data type conversion
(1) Implicit type conversion ： Safe switching , No data loss . For example, from a derived class to a base class , Small range type -> Wide range of types int->long,float->double, In some calculations, automatic conversion occurs
(2) Explicit type conversion ： Unsafe conversion , May cause data loss . such as double->int(3) Built in type conversion methods ：int.Parse()、ToString() etc.
namespace netBasic_learning
{
class Basic_dataType
{
public static void Main(String[] args)
{
// Data type conversion
// (1) Implicit type conversion ： Safe switching , No data loss . For example, from a derived class to a base class , Small range type -> Wide range of types int->long,float->double, In some calculations, automatic conversion occurs
// (2) Explicit type conversion ： Unsafe conversion , May cause data loss . such as double->int
double a = 3.1415;
int b = (int)a;// Rounding down , Lost precision
Console.WriteLine("Double->Int: {0}", b);
// (3) Built in type conversion methods
string num = "66";
Console.WriteLine("Int -> String: {0}",a.ToString());
Console.WriteLine("String -> Int: {0}", int.Parse(num));
//4. Constant ：const , Cannot be modified during operation
Console.ReadLine();
}
}
}
4. character string string type
One . character string ： Use string Keyword to declare a string variable .string Keywords are System.String Alias of class .
1. String construction ：
- ""：string str = "hello world!";
- +：string str = a + b;( String splicing )2. String common methods ：
- public static int Compare( string strA, string strB ): Compare two specified string object ( Press ASCII), And returns an integer representing their relative position in the arrangement order .
- public static string Concat( string str0, string str1 )： Connect two string object . amount to +
- public bool Contains( string value )： Determine whether the string contains a string value
- public bool EndsWith( string value )： Judge string Whether the object is in value ending .
- public bool StartsWith( string value )： Determines whether the beginning of the string instance matches the specified string .
- public bool Equals( string value )： Judge the current string Whether the object matches the specified string Object has the same value .
- public static string Format( string format, Object arg0 )： Replace one or more format items in the specified string with the string representation of the specified object .
- public int IndexOf( string value/char ch )： Returns the index of the first occurrence of the specified string in the instance , Index from 0 Start .
- public int LastIndexOf( string value/char value ): Returns the index of the last occurrence of the specified string in the instance , Index from 0 Start .
- public string Insert( int startIndex, string value )： Returns a new string , among , The specified string is inserted in the current string The specified index location of the object .
- public static string Join( string separator, string[] value )： Connect all elements in a string array , Separate each element with the specified separator .
- public string Remove( int startIndex )： Remove all characters in the current instance , Start at the specified location , Until the last position , And return a string .
- public string Replace( string oldValue, string newValue )： Put the present string In the object , All specified strings are replaced with another specified string , And return the new string .
- public string[] Split( params char[] separator )： Returns an array of strings , Include the current string Object , The substring is specified using Unicode Separated by elements in a character array .
- public char[] ToCharArray()： Returns a with the current string Of all characters in the object Unicode A character array .
- public string ToLower()/ToUpper()/Trim()
namespace netBasic_learning
{
class Basic_string
{
public static void mains(string[] args)
{
// （1） String construction ：
string a_str = "Hello,";
string b_str = "World!,Write the code,change the world.";
string strs = a_str + b_str;
Console.WriteLine(strs);
/**
*（2） String method 、 operation （ a key ）：
*/
//2. String comparison
string c_str = "Hello,";
if(a_str == c_str)//== In the quoted data , The comparison is the address . So two variables with the same data may be “ Unequal ”.
{
// But here it is the same , as a result of string Is a constant , The same address .
Console.WriteLine("== Comparative symbols ：a_str And c_str identical ");
}
if (a_str.Equals(c_str))//Equals The comparison is whether the values are the same , recommend ！
{
Console.WriteLine("Equals Comparison function ：a_str And c_str identical ");
}
int res = String.Compare(a_str, b_str);//a_str<b_str Is the more <0;a_str=b_str yes =0;a_str>b_str yes >0
Console.WriteLine(" Sorting result ： {0}",res);
//2. The string contains
if (strs.Contains("World"))
{
Console.WriteLine("{0} contain {1}", strs,"World");
}
//3. String acquisition
string child_str = strs.Substring(15);
Console.WriteLine(child_str);
//4. String merge
string[] str_arrays = { "hello", "world", "i'm", "OK" };
string join_str = String.Join("-", str_arrays);
Console.WriteLine(join_str);
//5. String segmentation
string[] str_list = join_str.Split('-');
foreach(string factor in str_list)
{
Console.WriteLine(factor);
}
//6. String formatting
Console.ReadKey();
}
}
}
3、 ... and .C# Calculations and conditions 、 loop
1. Calculation statement
1. Arithmetic operator ：+、-、*、/、%、++、--
2. Relational operator ：==、!=、>、<、>=、<=
3. Logical operators ：&&、||、!
4. An operation ：&( And , whole 1 only 1)、|( or , One 1 namely 1)、^( Exclusive or , Difference is 1)、<<( Move left , Right mend 0)、>>( Move right , Left complement 0)
5. Assignment operator ：+=、-=、/=、%=、&=、<<=
6. Other operators ：
（1）?: Ternary expression a==1?xxx:yyy
（2）& Address fetch
（3）* The pointer
（4）sizeof、typeof、is
namespace netBasic_learning
{
class Basic_calculate
{
public static void Main(string[] args)
{
// Arithmetic operations
double y = 5 / 2; // If / All methods are integers , The result of the operation is also an integer （ Rounding down ）
double y_2 = 5.0/2;// If / Method has a floating point number , The result of the operation is automatically converted to a large type
Console.WriteLine(y);
Console.WriteLine(y_2);
// summary ： Operation and Java almost -.-
Console.ReadLine();
}
}
}
2. To choice
One . conditional ：
（1）if...else if...else
（2）switch(Expression){
case condition1:
break;
case condition2:
break;
default:
}
namespace netBasic_learning
{
class Basic_calculate
{
public static void Main(string[] args)
{
double y = 5 / 2; // If / All methods are integers , The result of the operation is also an integer （ Rounding down ）
// conditional ：
if (y>0)
{
Console.WriteLine("y > 0");
}else if (y == 0)
{
Console.WriteLine("y = 0");
}
else
{
Console.WriteLine("y < 0");
}
Console.ReadLine();
}
}
}
3. Loop branches
One . Loop statement
(1) for：for( initialization , Judge , Cyclic operation ){ Loop statement }、foreach()
(2) while： As long as the given condition is true , Will repeatedly execute a target statement . Judge before you execute
（3）do..while： Check its condition at the end of the loop . Will ensure that at least one loop is executed .
(4) Loop control statement ：break Out of the loop ,continue Continue the cycle directly
namespace netBasic_learning
{
class Basic_calculate
{
public static void Main(string[] args)
{
// Loop statement
// (1)for：for( initialization , Judge , Cyclic operation ){ Loop statement }
// (2)while： As long as the given condition is true , Will repeatedly execute a target statement . Judge before you execute
// （3）do..while： Check its condition at the end of the loop . Will ensure that at least one loop is executed .
// (4) Loop control statement ：break Out of the loop ,continue Continue the cycle directly
for (int i = 0; i < 10; i++)
{
Console.WriteLine(i);
}
Console.ReadLine();
}
}
}
Four .C# Array
1. Null type
1. Null type （null）: Nullable types can represent values in the normal range of their underlying value types , Add one more null value .
(1) Declare nullable type ：
- The basic data ：? A single question mark is used to int、double、bool Etc. cannot be directly assigned to null The data type of null Assignment . such as ：int? num1 = null;
- Classes and objects ： Make a direct statement(2)null coalescing operator (??)： Judge if the value of the first operand is null, The operator returns the value of the second operand , Otherwise, return the value of the first operand .
- Use ：a = b ?? c
- The essence ：a = (b==null)?c:b
namespace netBasic_learning
{
class Basic_Arrays
{
public static void Main(string[] args)
{
//1. Null type （null）: Nullable types can represent values in the normal range of their underlying value types , Add one more null value .
// (1) Declare nullable type ：
int? num1 = null;// Can be empty int Type is null
int? num2 = 66;// Can be empty int Type does not take null value
double? num3 = null;
double? num4 = 3.1415;
Console.WriteLine(" Displays values of nullable types ： {0}, {1}, {2}, {3}",num1, num2, num3, num4);
if(num1 == null)// A null value judgment
{
Console.WriteLine("Int data num1 Null value ");
}
Rectangle rect = null;// class & Object null declaration
if(rect == null)// class & Object null value judgment
{
Console.WriteLine("Rectangle Class object rect It's empty ");
}
// (2)null coalescing operator (??)： Judge if the value of the first operand is null, The operator returns the value of the second operand , Otherwise, return the value of the first operand .
double? b = null;
double? c = 3.1415;
double? a = b ?? c;//b If it is empty, return c
Console.WriteLine("a Value ： {0}", a);
Console.ReadKey();
}
}
}
2. Array
1. Array ： An array is a store 【 Elements of the same type 】 A fixed size sequential set of
（1） Declaration array ：double[] arrays; Declaring an array does not initialize the array in memory .
（2） Initialize array ：double[] balance = new double[10]; Array is a reference type , So you need to use new Keyword to create an instance of the array .
（3） Array assignment ：
- Index assignment ： balance[0] = 3.14;
- Assign values to the array while declaring it ： double[] balance = { 2340.0, 4523.69, 3421.0};
- Create and initialize an array ： int [] marks = new int[5] { 99, 98, 92, 97, 95};
- Omit the size of the array ：int [] marks = new int[] { 99, 98, 92, 97, 95};
- Assign an array variable to another target array variable . under these circumstances , The target and source will point to the same memory location ( quote )：int[] score = marks;
（4） The data access 、 Traverse ：[] The subscript access +for、foreach loop（5） Multidimensional arrays ：int[,] a; Declare a two-dimensional array ,int[, ,] a; Declare a three-dimensional array
（6） Jagged arrays ： An interleaved array is an array of arrays . An interleaved array is a one-dimensional array , Each element is an array
- Statement ：int [][] scores;int One dimensional array of arrays , Declaring an array does not create an array in memory
- initialization ：int[][] scores = new int[5][]; There are five elements
- Initialize assignment ：int[][] scores = new int[2][]{new int[]{92,93,94},new int[]{85,66,87,88}};
- visit ：scores[i][j] Take the first place i The second... Of the subarray j Elements （ It's like a two-dimensional array ）
namespace netBasic_learning
{
class Basic_Arrays
{
public static void Main(string[] args)
{
//1. Array ： An array is a store 【 Elements of the same type 】 A fixed size sequential set of
// （1） Declaration array ：double[] arrays; Declaring an array does not initialize the array in memory .
// （2） Initialize array ：double[] balance = new double[10]; Array is a reference type , So you need to use new Keyword to create an instance of the array .
// （3） Array assignment ：
// - Index assignment ： balance[0] = 3.14;
// - Assign values to the array while declaring it ： double[] balance = { 2340.0, 4523.69, 3421.0};
// - Create and initialize an array ： int [] marks = new int[5] { 99, 98, 92, 97, 95};
// - Omit the size of the array ：int [] marks = new int[] { 99, 98, 92, 97, 95};
// - Assign an array variable to another target array variable . under these circumstances , The target and source will point to the same memory location ( quote )：int[] score = marks;
// （4） The data access 、 Traverse ：[] The subscript access +for、foreach loop
int[] List = new int[10];
for(int i = 0; i < List.Length; i++)
{
List[i] = i*2;
}
foreach(int j in List)
{
Console.WriteLine("Element = {0}",j);
}
// （4） Multidimensional arrays ：int[,] a; Declare a two-dimensional array ,int[, ,] a; Declare a three-dimensional array
int[,] matrix = new int[3, 4];// initialization 3x4 Two dimensional array of
int[,] matrix_2 = new int[3, 4]{// Initialize and assign
{0,1,2,3 }, // Initializing page 0 That's ok
{4,5,6,7}, // Initializing page 1 That's ok
{8,9,10,11} // Initializing page 2 That's ok
};
for(int i = 0; i < matrix_2.GetLength(0); i++)// Loop through multidimensional arrays
{
for(int j = 0; j < matrix_2.GetLength(1); j++)
{
Console.WriteLine(" matrix ({0},{1}) The value of is {2}", i,j, matrix_2[i,j]);
}
}
// （5） Jagged arrays ： An interleaved array is an array of arrays . An interleaved array is a one-dimensional array , Each element is an array
// - Statement ：int [][] scores;int One dimensional array of arrays , Declaring an array does not create an array in memory
// - initialization ：int[][] scores = new int[5][]; There are five elements
// - Initialize assignment ：int[][] scores = new int[2][]{new int[]{92,93,94},new int[]{85,66,87,88}};
// - visit ：scores[i][j] Take the first place i The second... Of the subarray j Elements （ It's like a two-dimensional array ）
int[][] scores = new int[5][];
for (int i = 0; i < scores.Length; i++)
{
if (i <= 2) scores[i] = new int[3];
else scores[i] = new int[5];
for(int j = 0; j < scores[i].Length; j++)
{
scores[i][j] = i * j + 6;
}
}
for (int i = 0; i < scores.Length; i++)
{
for (int j = 0; j < scores[i].Length; j++)
{
Console.WriteLine(" Subarray {0} Subscript {1} The value of is {2}", i, j, scores[i][j]);
}
}
Console.ReadKey();
}
}
}
（7）Array class ：Array Class is C# The base class for all arrays in , Provides many properties and methods
- Array.Clear: Depending on the type of element , Set the element of a range in the array to zero 、 by false Or for null.
- Array.IndexOf(Array, Object): Search for the specified object , Back to the whole [ One dimensional array ] The first index in .
- Array.Reverse(Array): Reverse the order of elements in an entire one-dimensional array .
- Array.Sort(Array): Use the... Of each element of the array IComparable Implement to sort the elements of the entire one-dimensional array .
namespace netBasic_learning
{
class Basic_Arrays
{
public static void Main(string[] args)
{
// （6）Array class ：Array Class is C# The base class for all arrays in , Provides many properties and methods
// - Array.Clear: Depending on the type of element , Set the element of a range in the array to zero 、 by false Or for null.
// - Array.IndexOf(Array, Object): Search for the specified object , Back to the whole [ One dimensional array ] The first index in .
// - Array.Reverse(Array): Reverse the order of elements in an entire one-dimensional array .
// - Array.Sort(Array): Use the... Of each element of the array IComparable Implement to sort the elements of the entire one-dimensional array .
int[] list = { 34, 72, 13, 44, 25, 30, 10 };
Console.Write(" The original array ： ");
foreach (int i in list)
{
Console.Write(i + " ");// Don't wrap output
}
Console.WriteLine();// Output line feed
// Reverse array
Array.Reverse(list);// Change the original array
Console.Write(" Reverse array ： ");
foreach (int i in list)
{
Console.Write(i + " ");
}
Console.WriteLine();
// Sort array
Array.Sort(list);// Change the original array , Default from small to large
Console.Write(" Sort array ： ");
foreach (int i in list)
{
Console.Write(i + " ");
}
Console.ReadKey();
}
}
}
5、 ... and . Lists and dictionaries
1. list ArrayList
1.ArrayList： Dynamic array list collection , Be similar to Java Of List<Object>
（1） initialization ：ArrayList Is a class / object , Need to use new Keyword initialization , And there is no need to specify the size （ Dynamic expansion ） ArrayList array = new ArrayList();
（2） characteristic ：
- Dynamic extension of length , There is no need to specify ;
- Use when storing data Object type , So it can store many different data at the same time （int、double、class、string）
- Not type safe , Type matching errors may occur ; There are frequent packing and unpacking operations , Poor performance
（3） Use ：
- Item[Int32] Gets or sets the element at the specified index .
- Count obtain ArrayList Number of elements actually contained in .
- public virtual int Add( object value ); stay ArrayList Add an object at the end of .
- public virtual void Clear(); from ArrayList Remove all elements from .
- public virtual void Insert( int index, object value ); stay ArrayList At the specified index of , Insert an element .
- public virtual void Remove( object obj ); from ArrayList Remove the first occurrence of the specified object .
namespace netBasic_learning
{
//1.ArrayList： Dynamic array list collection , Be similar to Java Of List<Object>
class ArrayList_Use
{
public static void mains(string[] args)
{
ArrayList arrayList = new ArrayList();
arrayList.Add(2);
arrayList.Add(3.1415);
arrayList.Add("hello world");
Console.WriteLine("ArrayList length ： " + arrayList.Count);
Console.WriteLine("ArrayList[0]： " + arrayList[0]);
Console.WriteLine("ArrayList[1]： " + arrayList[1]);
Console.WriteLine("ArrayList[2]： " + arrayList[2]);
Console.ReadKey();
}
}
}2. list List
2.List：List It is also a dynamic list collection , Be similar to ArrayList, But you must provide generics
（1） Definition ： In order to solve ArrayList The type of is not safe ,C# Provides List list ,List A generic type must be provided when declaring a list , namely List The stored data must be the data of the generic type .
（2） initialization ：List<int> list = new List<int>();
（3） The essence ：List In fact, in the ArrayList On the basis of , Added type restrictions , It is recommended to use in the future List
（4） Use ： And ArrayList similar , Note that generics can also be custom classes ,List You can also store objects ！
namespace netBasic_learning
{
//2.List：List It is also a dynamic list collection , Be similar to ArrayList, But you must provide generics
// （1） Definition ： In order to solve ArrayList The type of is not safe ,C# Provides List list ,List A generic type must be provided when declaring a list , namely List The stored data must be the data of the generic type .
// （2） initialization ：List<int> list = new List<int>();
// （3） The essence ：List In fact, in the ArrayList On the basis of , Added type restrictions , It is recommended to use in the future List
// （4） Use ： And ArrayList similar , Note that generics can also be custom classes ,List You can also store objects ！
class List_Use
{
public static void mains(string[] args)
{
List<int> list = new List<int>();
for(int i = 0; i < 10; i++)
{
list.Add(i + 1);
}
for(int i = 0; i < list.Count; i++)
{
if (list[i] % 2!=0)
{
list[i] *= 2;
}
}
foreach(int val in list)
{
Console.Write(val + " ");
}
Console.WriteLine();
list.Clear();
Console.WriteLine(" Length after emptying ： " + list.Count);
Console.ReadLine();
}
}
}
3. Dictionaries Dictionary
3.Dictionary：Dictionary Is a dictionary type consisting of key value pairs , Be similar to Java Of Map
（1） initialization ：Dictionary Also object , Need to use new keyword . At the same time, you need to specify the generic type of key value pair during initialization Dictionary<string,int> dir = new Dictionary<string,int>();
（2） characteristic ：
- Dictionary Every element in it is a key value pair ( It's made up of two elements ： Key and value ), Can pass Dictionary[key] To take a value
- Dictionary The inner key must be unique , And values don't need to be unique
（3） Use ：
- Count Get included in Dictionary<TKey, TValue> The key / The right number .
- Keys Get contains Dictionary<TKey, TValue> The set of keys in .
- Values Get contains Dictionary<TKey, TValue> The set of values in .
- Add Adds the specified key and value to the dictionary .
- Clear from Dictionary<TKey, TValue> Remove all keys and values from .
- ContainsKey determine Dictionary<TKey, TValue> Whether to include the specified key .
- GetEnumerator Return to loop access Dictionary<TKey, TValue> The enumerator of
- Remove from Dictionary<TKey, TValue> Remove the value of the specified key from the .
namespace netBasic_learning
{
//3.Dictionary：Dictionary Is a dictionary type consisting of key value pairs , Be similar to Java Of Map
// （1） initialization ：Dictionary Also object , Need to use new keyword . At the same time, you need to specify the generic type of key value pair during initialization Dictionary<string,int> dir = new Dictionary<string,int>();
// （2） characteristic ：
// - Dictionary Every element in it is a key value pair ( It's made up of two elements ： Key and value ), Can pass Dictionary[key] To take a value
// - Dictionary The inner key must be unique , And values don't need to be unique
// （3） Use ：
// - Count Get included in Dictionary<TKey, TValue> The key / The right number .
// - Keys Get contains Dictionary<TKey, TValue> The set of keys in .
// - Values Get contains Dictionary<TKey, TValue> The set of values in .
// - Add Adds the specified key and value to the dictionary .
// - Clear from Dictionary<TKey, TValue> Remove all keys and values from .
// - ContainsKey determine Dictionary<TKey, TValue> Whether to include the specified key .
// - GetEnumerator Return to loop access Dictionary<TKey, TValue> The enumerator of
// - Remove from Dictionary<TKey, TValue> Remove the value of the specified key from the .
class Dictionary
{
public static void Main(string[] args)
{
Dictionary<string, int> dictionary = new Dictionary<string, int>();
dictionary.Add("wangxin", 99);//Add assignment ,Add Assignment cannot be added key Duplicate items
dictionary["shayuan"] = 100;//= assignment ,= Assignment can add key Duplicate item , Will overwrite the original data
if (dictionary.ContainsKey("wangxin"))// Does it include key
{
Console.WriteLine("Dictionary length ： " + dictionary.Count);
Console.WriteLine("wangxin is {0}", dictionary["wangxin"]);
dictionary.Remove("wangxin");// Delete key
}
if (dictionary.ContainsKey("shayuan"))
{
Console.WriteLine("Dictionary length ： " + dictionary.Count);
Console.WriteLine("shayuan is {0}", dictionary["shayuan"]);
}
//Console.WriteLine("wangxin is {0}", dictionary["wangxin"]);// Accessing nonexistent data will result in an exception
if (!dictionary.ContainsKey("wangxin"))
{
Console.WriteLine("wangxin is removed!");
}
// Traverse Dictionary
// Traverse key
foreach (string key in dictionary.Keys)
{
Console.WriteLine("Key = {0}", key);
}
// Traverse value
foreach (int value in dictionary.Values)
{
Console.WriteLine("value = {0}", value);
}
// Ergodic dictionary
foreach (KeyValuePair<string, int> kvp in dictionary)
{
Console.WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value);
}
// Add existing elements try...catch.. Handling exceptions
try
{
dictionary.Add("txt", 99);
}
catch (ArgumentException)
{
Console.WriteLine("An element with Key = \"txt\" already exists.");
}
Console.ReadKey();
}
}
}
6、 ... and . Class to inherit
1. The basic concept of class
1. Class encapsulation
（1） Access modifier ： The default access identifier of the class is internal, The default access identifier for a member is private.
- public： All objects can access ;
- private： The object itself can be accessed inside the object ;
- protected： Only objects of this class and its subclasses can access
- internal： Objects of the same assembly can access ; Can be defined in the 【 In app 】 Any class or method access .
- protected internal： Access is limited to the current assembly or type derived from the containing class .（protected and internal Union ）
（2） Method ： Class , It mainly refers to the transfer method of method parameters
- Value passed ： In this way, the actual value of the parameter is copied to the formal parameter of the function , Arguments and formal parameters use two different values in memory . under these circumstances , When the value of a formal parameter changes , Does not affect the value of the argument
- reference (ref)： In this way, the reference of the memory location of the parameter is copied to the formal parameter . It means , When the value of a formal parameter changes , It also changes the value of the argument .
- Output parameters (out)： Multiple values can be returned in this way . Pass on out When the defined parameter goes in, the parameter must be initialized inside the function . Otherwise, it cannot be compiled .
- Array pass value ： You can pass a pointer to an array to a function by specifying an array name without an index .
Be careful ：ref and out All the data is transferred to , Because of the address , To modify the source data .2. Basic parameters of class
（1） Constructors ： Automatically execute when initializing an object , A parameterless construct is provided by default Object(){}
（2） Destructor ： Automatically execute when destroying objects ~Object(){}
（3） Static member variable ： static Keyword defines a class member as static , Static member variables belong to class , Can be initialized and used anywhere
（4） Static member functions ：static Keyword defines a class member as static , Static member variables belong to class , Static member functions can only access static variables
namespace netBasic_learning
{
//1. Class encapsulation
// （1） Access modifier ： The default access identifier of the class is internal, The default access identifier for a member is private.
// - public： All objects can access ;
// - private： The object itself can be accessed inside the object ;
// - protected： Only objects of this class and its subclasses can access
// - internal： Objects of the same assembly can access ; Can be defined in the 【 In app 】 Any class or method access .
// - protected internal： Access is limited to the current assembly or type derived from the containing class .（protected and internal Union ）
// （2） Method ： Class , It mainly refers to the transfer method of method parameters
// - Value passed ： In this way, the actual value of the parameter is copied to the formal parameter of the function , Arguments and formal parameters use two different values in memory . under these circumstances , When the value of a formal parameter changes , Does not affect the value of the argument
// - reference (ref)： In this way, the reference of the memory location of the parameter is copied to the formal parameter . It means , When the value of a formal parameter changes , It also changes the value of the argument .
// - Output parameters (out)： Multiple values can be returned in this way . Pass on out When the defined parameter goes in, the parameter must be initialized inside the function . Otherwise, it cannot be compiled .
// - Array pass value ： You can pass a pointer to an array to a function by specifying an array name without an index .
// Be careful ：ref and out All the data is transferred to , Because of the address , To modify the source data .
class A
{
public int _a;
public int _b;
// Value passed
public void sum(int a,int b)
{
a += b;
Console.WriteLine(" Sum in value transfer function a = {0}", a);
}
// reference
public void sum(ref int a,ref int b)
{
a += b;
Console.WriteLine(" Sum inside the reference transfer function a = {0}", a);
}
// Output parameters
public void sum(int a,int b,out int c)
{
c = a + b;
}
// class / Object delivery ( Object value transfer = Pass value by reference )
public void swap(A obj)
{
int temp = obj._a;
obj._a = obj._b;
obj._b = temp;
}
// Array pass value
public void sumAndClear(int[] arrays)
{
int sum = 0;
for(int i = 0; i < arrays.Length; i++)
{
sum += arrays[i];
arrays[i] = 0;
}
Console.WriteLine(" Array sum sum = {0}", sum);
}
public static void Main(string[] args)
{
A a_obj = new A();
// Value passed
int a = 3, b = 4;
Console.WriteLine(" Value transfer initial data before summation a = {0},b = {1}", a,b);
a_obj.sum(a, b);
Console.WriteLine(" Initial data after summation of value transfer a = {0},b = {1}", a, b);
// reference
Console.WriteLine(" Reference passes the initial data before summation a = {0},b = {1}", a, b);
a_obj.sum(ref a, ref b);
Console.WriteLine(" The initial data after the sum is passed by reference a = {0},b = {1}", a, b);
// Output parameters
int res;
Console.WriteLine(" Output initial data before parameter summation a = {0},b = {1}", a, b);
a_obj.sum( a, b,out res);
Console.WriteLine(" The initial data after the sum is passed by reference a = {0},b = {1},res = {2}", a, b,res);
// Object delivery
a_obj._a = 3;
a_obj._b = 4;
Console.WriteLine(" The object passes the initial data before exchange a = {0},b = {1}", a_obj._a, a_obj._b);
a_obj.swap(a_obj);
Console.WriteLine(" Object transfers the initial data after exchange a = {0},b = {1}", a_obj._a, a_obj._b);
// Array passing
int[] arr = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
Console.Write(" Before array value transfer ： ");
foreach(int fac in arr) Console.Write(fac + " ");
Console.WriteLine();
a_obj.sumAndClear(arr);
Console.Write(" After the array passes values ： ");
foreach (int fac in arr) Console.Write(fac + " ");
Console.ReadLine();
}
}
//2. Basic parameters of class
// （1） Constructors ： Automatically execute when initializing an object , A parameterless construct is provided by default Object(){}
// （2） Destructor ： Automatically execute when destroying objects ~Object(){}
// （3） Static member variable ： static Keyword defines a class member as static , Static member variables belong to class , Can be initialized and used anywhere
// （4） Static member functions ：static Keyword defines a class member as static , Static member variables belong to class , Static member functions can only access static variables
class B
{
public static int cnt = 0;
private double val;
public B()
{
val = 0;
cnt++;
Console.WriteLine(" The first {0} individual B, Parameter free constructor Val = {1}",cnt,val);
}
public B(double _val = 0)
{
val = _val;
cnt++;
Console.WriteLine(" The first {0} individual B, There are parameter constructors Val = {1}", cnt,val);
}
public double getVal()
{
return this.val;
}
public static int getCntOfB()
{
return cnt;
}
~B()
{
cnt--;
Console.WriteLine(" The destructor executes ");
}
public static void Main(string[] args)
{
B b_1 = new B();
Console.WriteLine(b_1.getVal());
B b_2 = new B(3.14);
Console.WriteLine(b_2.getVal());
Console.WriteLine(B.getCntOfB());
Console.ReadKey();
}
}
}
2. Class inheritance
3. Class inheritance Child:Parent
（1）C# Only single inheritance is supported , But multiple inheritance can be implemented through interfaces
（2） Derived classes inherit the base class's public、protected、internal Member variables and member methods .
（3） If not specified , When you create a subclass object and call the subclass constructor , The parameterless constructor of the parent class will be called first by default
namespace netBasic_learning
{
//3. Class inheritance Child:Parent
// （1）C# Only single inheritance is supported , But multiple inheritance can be implemented through interfaces
// （2） Derived classes inherit the base class's public、protected、internal Member variables and member methods .
// （3） If not specified , When you create a subclass object and call the subclass constructor , The parameterless constructor of the parent class will be called first by default
class Shape
{
protected double length;
protected double width;
public Shape(double len,double wid)
{
length = len;
width = wid;
}
public double GetArea()
{
return length * width;
}
public void Display()
{
Console.WriteLine(" length ： {0}", length);
Console.WriteLine(" Width ： {0}", width);
Console.WriteLine(" area ： {0}", GetArea());
}
}
class Cube:Shape
{
private double height;
public Cube(double len,double wid,double hei): base(len, wid)//base(x,y) Initialize parent class parameters , Execute before subclass
{
height = hei;
}
public double GetVolume()
{
return height * GetArea();
}
public void Display()
{
base.Display();// adopt base To refer to the parent class of the current object
Console.WriteLine(" Volume ： {0}", GetVolume());
}
public static void Main(string[] args)
{
Cube cube = new Cube(2, 3, 4);
cube.Display();// Call the override method of the subclass
Console.ReadKey();
}
}
}
7、 ... and . many state
1. polymorphic ： Polymorphism is the ability of the same behavior to have multiple different forms or forms according to different scenarios .
（1） Static polymorphism ： Function response occurs at compile time .
- function overloading ： There are multiple definitions of the same function name . It can be that the parameter types in the parameter list are different , It can also be that the number of parameters is different . Cannot overload function declarations with only different return types .
- Operator overloading ： Can redefine or overload C# The operators built into . By keyword operator Defined by the symbol followed by the operator , Also include public and static Modifier .
namespace netBasic_learning
{
//1. polymorphic ： Polymorphism is the ability of the same behavior to have multiple different forms or forms according to different scenarios .
// （1） Static polymorphism ： Function response occurs at compile time .
// - function overloading ： There are multiple definitions of the same function name . It can be that the parameter types in the parameter list are different , It can also be that the number of parameters is different . Cannot overload function declarations with only different return types .
// - Operator overloading ： Can redefine or overload C# The operators built into . By keyword operator Defined by the symbol followed by the operator , Also include public and static Modifier .
class Vector
{
private int x;
private int y;
public Vector()
{
x = 0;
y = 0;
}
public Vector(int _x,int _y)
{
x = _x;
y = _y;
}
public int getX() { return x; }
public int getY() { return y;}
public void setX(int x) { this.x = x; }
public void setY(int y) { this.y = y; }
public void Display()
{
Console.WriteLine("Vector({0},{1})", x, y);
}
// heavy load + Operator to put two Vector Add objects ( You can directly access private)
public static Vector operator +(Vector a, Vector b)
{
Vector C = new Vector();
C.x = a.x + b.x;
C.y = a.y + b.y;
return C;
}
// heavy load - Operator to put two Vector Object subtraction ( You can directly access private)
public static Vector operator -(Vector a, Vector b)
{
Vector C = new Vector();
C.x = a.x - b.x;
C.y = a.y - b.y;
return C;
}
// heavy load * Operator to put two Vector Multiply objects ( You can directly access private)
public static int operator *(Vector a, Vector b)
{
return a.x * b.x + a.y * b.y;
}
public static void Main(string[] args)
{
Vector a = new Vector(2, 3);
Vector b = new Vector(3, 4);
//+ Law
Vector c = a + b;
c.Display();
//- Law
c = a - b;
c.Display();
//* Law
int res = a * b;
Console.WriteLine(res);
Console.ReadKey();
}
}
}（2） Dynamic polymorphism ： The response of the function occurs at run time .
- Virtual method （virtual ）： Defining a subclass can override methods that override the parent class , The call to a virtual method occurs at run time . Subclasses need to use override Statement
+ The parent class defines the virtual method , Subclasses can override the virtual methods of the parent class , It is also possible not to implement rewriting . If I rewrite it , After creating the subclass object , Whether it's a parent class pointer or a subclass , Calling virtual methods will perform the override of subclasses .
+ The parent class defines the virtual method , There must be an implementation of the parent class , It is a normal function in the parent class .
- abstract （abstract ）： abstract abstract Keywords can act on methods , It can also work on classes . Subclasses need to use override Statement
+ The parent class abstract method does not implement , Only the statement . The subclass must implement the abstract method of the parent class
+ Any method in a class is abstract , The class must be declared as an abstract class . That is, abstract methods can only be defined in abstract classes
+ Abstract class cannot be instantiated , But it can point to subclass instances . Subclasses that do not implement abstract methods will also become abstract classes .
- summary ： In short , Abstract methods need subclasses to implement . Virtual methods are already implemented , Can be overridden by subclasses , You can also not cover , Depends on demand . Both abstract and virtual methods can be overridden by derived classes .
namespace netBasic_learning
{
// Dynamic polymorphism ： The response of the function occurs at run time .
// - Virtual method （virtual ）： Defining a subclass can override methods that override the parent class , The call to a virtual method occurs at run time . Subclasses need to use override Statement
// + The parent class defines the virtual method , Subclasses can override the virtual methods of the parent class , It is also possible not to implement rewriting . If I rewrite it , After creating the subclass object , Whether it's a parent class pointer or a subclass , Calling virtual methods will perform the override of subclasses .
// + The parent class defines the virtual method , There must be an implementation of the parent class , It is a normal function in the parent class .
// - abstract （abstract ）： abstract abstract Keywords can act on methods , It can also work on classes . Subclasses need to use override Statement
// + The parent class abstract method does not implement , Only the statement . The subclass must implement the abstract method of the parent class
// + Any method in a class is abstract , The class must be declared as an abstract class . That is, abstract methods can only be defined in abstract classes
// + Abstract class cannot be instantiated , But it can point to subclass instances . Subclasses that do not implement abstract methods will also become abstract classes .
// - summary ： In short , Abstract methods need subclasses to implement . Virtual methods are already implemented , Can be overridden by subclasses , You can also not cover , Depends on demand . Both abstract and virtual methods can be overridden by derived classes .
abstract class Animal
{
// abstract class ： Contains at least one abstract method , But it's not just about abstract methods
protected string name;
public Animal(string _name)
{
name = _name;
}
// Abstract method ： It's called
abstract public void shout();
// Virtual method
virtual public void eat()
{
Console.WriteLine("{0} is eating",name);
}
}
class Dog : Animal
{
public Dog(string name):base(name)
{
}
// Implementing abstract classes
public override void shout()
{
Console.WriteLine("A Dog {0} is wangwang",name);
}
// Override override virtual function
public override void eat()
{
base.eat();
Console.WriteLine("A Dog {0} is eat bone", name);
}
}
class Cat : Animal
{
public Cat(string name) : base(name)
{
}
// Implementing abstract classes
public override void shout()
{
Console.WriteLine("A Cat {0} is miaomiao", name);
}
// Override override virtual function
public override void eat()
{
base.eat();
Console.WriteLine("A Cat {0} is eat fish", name);
}
public static void Main(string[] args)
{
Animal[] animals = new Animal[2] { new Dog("tom"), new Cat("marry") };
foreach(Animal animal in animals)
{
animal.shout();
animal.eat();
}
Console.ReadKey();
}
}
}
2. Interface （interface）： Interfaces are similar to abstract classes , But all the methods in the interface are abstract
（1） Interface cannot be instantiated , Inherited interfaces must implement all abstract methods （ Don't declare override）, Interfaces can point to subclasses （ polymorphic ）
（2） The interface is declared as public
（3） Interfaces can inherit more , solve C# The inner class can inherit multiple base classes at the same time .
（4） Interface can inherit interface
namespace netBasic_learning
{
//2. Interface （interface）： Interfaces are similar to abstract classes , But all the methods in the interface are abstract
// （1） Interface cannot be instantiated , Inherited interfaces must implement all abstract methods （ Don't declare override）, Interfaces can point to subclasses （ polymorphic ）
// （2） The interface is declared as public
// （3） Interfaces can inherit more , solve C# The inner class can inherit multiple base classes at the same time .
// （4） Interface can inherit interface
interface Parent
{
void disPlay();
}
class Child : Parent
{
public void disPlay()
{
Console.WriteLine("child is display!");
}
}
}
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