C Getting Started tutorial

C# Introduction to small tutorial

One 、C# The history of development
C# yes .net One of several languages supported by the development platform . yes Microsoft Specially for .net
A new programming language for platform development , The syntax is similar to C Language .
1998 year ,Delphi First design C# Language version
2002 year , Released the first C# edition (1.0)
Two 、C# Can do
1.Windows Window application .Microsoft office,Windows Appearance Application ( Button , Tools )
2.web Applications ( mailbox 、 Forum 、 Website )
3. Network database and other applications
4.web Services and various distributed applications
3、 ... and 、C# Program structure
One C# The procedure mainly includes the following parts :
1. Namespace declaration
2. One class
3. Method
4. attribute
5.Main Method
6. sentence , expression
7. notes

using System;–> introduce System Namespace (C Language ：#include<stdio.h>)
using System.Collections.Generic;–> introduce C# Generic namespace
using System.Linq;–> The main function is to query the collection
using System.Text;–> Output text type
using System.Threading.Tasks;–> Asynchronous operations

namespace cxsw–> Create a namespace
{
class demo1–> Create a file called demo1 Class
{
static void Main(string[] args)–>main Method , Program entry
{
}
}
}

main There are four ways to write a method ：
1)static void Main(){}string[] args
2)static void Main(){}
3)static int Main(String[] args){}
4)static int Main(){}

Be careful ：
C# The first letter of the main method name must be capitalized :Main(), And there must be static keyword
Four . Output from console ：
1. Output string constant
Console.WriteLine(“ String constant ”);
2. Output a single variable
Console.WriteLine( Variable );
3. Use connectors (+) Mix output strings and variables
Console.WriteLine(“ character string ”+ Variable );
4. Use format placeholders to mix output strings and variables
Console.WriteLine(“ character string {0},{1}”, expression 1, expression 2);
5、 ... and . Input... From the console ：
1) Input string type
Define a variable of type string , Accept the string entered by the user
String name;
Give the user a hint , Prompt the user to enter
Console.WriteLine(“ Please enter a name ：”);
Store the user's input into variables
name=Console.Readline();
2) Convert a string into a number
age=int.Parse(Console.Readline());
6、 ... and . notes
Annotation mode ：
Single-line comments ：//
Multiline comment ：/……/
Documentation Comments ：/// xml notes
using System;namespace cxsw { // Create a namespace
class Test101HelloWorld { // Create a class
static void Main(string[] args) { // The main function
// Output
Console.WriteLine(“ Today's first day ”); // Console output
int i = 1;
Console.WriteLine(i); // Output variables
Console.WriteLine(“i The value of is :”+i);
Console.WriteLine("1+1={0},22={1}",1+1,22);
// Input
string name;
Console.WriteLine(“ Please enter your name :”);
name = Console.ReadLine();
Console.WriteLine(“ The name entered by the user is :”+name);
// Convert a string to a number
Console.WriteLine(“ Please enter a number to convert to a string :”);
int age = int.Parse(Console.ReadLine());
Console.WriteLine(“ The string that is converted to a number is :”+age);

        //Console.ReadKey();// in the light of VS.NET User 
        // This causes the program to wait for a key action , Prevent the program from VisualStudio.NET
        // The screen will run quickly and close when starting 
        // That is to say, the program execution will wait for you to press the key before exiting 
    }
}}

Chapter two : Data type constant variable
One . data type
（1） Integer types
Mathematical integers can range from negative infinity to positive infinity , But the storage unit of the computer is limited ,
Therefore, the value of integer type provided by computer language is always within a certain range .
C# There are eight data types ：
Short byte type （sbyte）, Byte type （byte）, Short （stort）, Unsigned short （ustort）,
integer （int）, Unsigned integer （unit）, Long integer （long）, Unsigned long （ulong）.

（2） Character type
In addition to digital , The information processed by the computer also includes characters . Characters mainly include numeric characters , English characters ,
Expression characters, etc ,C# The character classes provided are in accordance with internationally recognized standards , use Unicode Character set .
Character book data occupies two bytes of memory , It can be used to store Unicode A character in a character set （
Be careful , Just one character , Not a string ）.

（3） Real number type
C# There are three types of real numbers ：float（ Single precision type ）,doudle（ Double precision type ）,decimal（ Decimal type ）.

（4） Boolean type
Boolean type is used to represent “ really ” and “ false ” Of two concepts , stay C# In the use true and false To express .

1. Common data types
Integers ：(4 Kind of )
int(32 An integer )、short(16)、long(64)、byte(8)
floating-point ：(3 Kind of )
float(32 Bit floating point , Accurate to the decimal point 7 position )
double(64 Bit floating point , Accurate to the decimal point 15~20 position )
decimal(128 Bit floating point , Accurate to the decimal point 28~29 position )
Boolean type ：bool true、false
Character ：char( Single character , Store in single quotation marks )
String type ：string( Double quotes )

2. Data type conversion
The size relationship between data types ：
byte–>short–>int–>float–>double–>decimal
1. Implicit type transformation
The transformation from low type to high type
Be careful ： The two data types to be converted must be compatible
2. Explicit type conversion ( Forced type conversion )
The transformation from high type to low type
1) utilize Parse Methods to transform
double d1=2.23;
int i1=int.Parse(d1);
2) Use convert Forced conversion of the provided class
grammar ：
ToDouble( Variable )

			double d = 23.5;
			int i;
			i = (int)d;

3. Reference type
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;
namespace Csp Personal course preparation . Chapter 2 data type variables {
class Test201 data type
{
static void Main(string[] args)
{
// data type
int age;// Used to indicate age
double score;// Used to express scores
char gender;// Used to indicate gender
bool b;// Used to indicate true or false
}
}}

Two . Constant
grammar ：
const data type Variable name = Constant values ;
When declaring and initializing variables , Add the keyword before the variable const, You can specify a variable as a constant .
In the process of using , Constant values do not change , Constant values are not allowed to be modified later , The naming conventions of constants and variables are the same .
using System;namespace Csp Personal course preparation . Chapter 2 data type variables {
class Test202 {
const double pi = 3.14; // Define constants
static void Main(string[] args) {
Console.WriteLine(pi);
}
}}
3、 ... and . Variable
1. Declaration of variables
Variable type Variable name ;
int num;
Variable type Variable name = A variable's value ;
Room type Your room number, = Check in guests ;
2. Variable name
1) Hump nomenclature ： The first letter of the middle word is capitalized
demodirect–>demoDirect
2) PASCAL nomenclature ： The first letter of each word is capitalized
demodirect–>DemoDirect
3. Naming rules for variables
1) By letter 、 Numbers 、 Underline composition , Cannot start with a number
2) You cannot use reserved words as variable names (console)
3) English words are recommended
4) Variable names are case sensitive
4. matters needing attention ：
1) Undeclared variables cannot be used
2) Unassigned variables cannot be output
3) You can declare multiple variables at once
4) You can declare it before you assign it , It can also be declared and initialized at the same time
using System;namespace Csp Personal course preparation . Chapter 2 data type variables {
class Test203 {
static void Main(string[] args) {
// The variables defined in the function body are local variables Can only be used in the body of the current function
// Defining variables
int a;
a = 10;
Console.WriteLine(“ Variable a The value of is :”+ a);
int b = 20;
Console.WriteLine(“ Variable b The value of is :”+b);
b = 40;
Console.WriteLine(“ Variable b The modified value is :”+ b);
int c, d;
c = 3;
d = 4;
Console.WriteLine(“ Variable c The value of is :”+c+“, Variable d The value of is :”+d);
int e = 1, f = 2;
Console.WriteLine(“ Variable e The value of is :”+e+“, Variable f The value of is :”+f);
}
}}
using System;namespace Csp Personal course preparation . Chapter 2 data type variables {
class Test204 {
static int i; // The variables defined outside the function are global variables You can use... In the current file
static void Main(string[] args)
{
// The variables defined in the function body are local variables Can only be used in the body of the current function
// Defining variables
int a = 10;
Console.WriteLine(“ Variable a Output :”+a);

		i = 30;
		Console.WriteLine(" Constant output :"+i);
	}
	void eat(){
		//a = 11; // Prompt undefined access is not available 
		i = 31; // No error is prompted to prove that you can access 
	}

}}

Four . matters needing attention
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;
namespace Csp Personal course preparation . Chapter 2 data type variables {
class Test205{
static void Main(string[] args)
{
short s = 1;
int i = 2;
long l = 3;
char ch = ‘a’;
Console.WriteLine(s + " " + i + " " + l + " " + ch);
//i = 2200000000;// When selecting data type Note whether it is out of range
// If out of range, error

		float ff = 3.14f; // Floating point number type followed by f
		double dd = 3.14;
		Console.WriteLine(ff + " " + dd);

		//char type 
		char cs = 'a';//char The value of type should be enclosed in single quotation marks 
		char cc = ' ';//char The value of type can't have nothing, even a space 
		char ccc = '\n';// Indicates the escape character 
		char c1 = (char)97;//ASCII code 
		Console.WriteLine(cs+" "+cc+" "+ccc+" "+c1);

		// Data type conversion 
		short st1 = 2;
		int it1 = st1;// Implicit conversion 
		Console.WriteLine("it1 The value of is :"+it1);
		double db1 = 25.5;
		int it2 = (int)db1;// Coercive transformation 
		Console.WriteLine("it2 The value of is :"+it2);
	}
}}

5、 ... and .ASCII clock

6、 ... and . Escape character

The third chapter : Operator
One . Arithmetic operator

• • • / % ++ –
      + The usage of number ：
      1) Add two numbers
      2) String connection
      ++、– Compound operation ：
      1)++ before ： Calculate first , Post assignment
      2)++ After ： Assign first , Post operation
      using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;
      namespace Csp Personal course preparation . Chapter 3 operators and expressions {
      class Test301 Arithmetic operator {
      static void Main(string[] args) {
      int A = 10, B = 5;
      // Various operations of arithmetic operators
      Console.WriteLine(“A=10,B=5”);
      Console.WriteLine(“A+B=”+(A + B));
      Console.WriteLine(“A-B=”+(A - B));
      Console.WriteLine(“A*B=”+(A * B));
      Console.WriteLine(“A/B=”+(A / B));
      // modulus , The expression says A%%B, Two of them % Indicates the output of a %
      Console.WriteLine(“A%B=”+(A % B));

       int a = 1, b = 2, c = 3, d = 0;
       Console.WriteLine("a,b,c The value of is :"+a+" "+b+" "+c);
       Console.WriteLine("a++ The value of is :"+(a++));
       Console.WriteLine("a The value of is :"+a);
       Console.WriteLine("++a The value of is :"+(++a));
       Console.WriteLine("a The value of is :"+a);
       a = 1; b = 2; c = 3; d = 0;
       //a = 3; b = 3; c = 3;
       //   1    2    3    3    3
       d = a++ + a + ++b + b + ++a;  // In the next calculation, we will get all the values after adding one 
       Console.WriteLine("d The value of is :"+d);//12
      

      }
      }}

Two . Relational operator
( Comparison is equal ) != > < >= <=
1
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;/**

• Relational operator
• == != > < >= <=
  **/namespace Csp Personal course preparation . Chapter 3 operators and expressions {
  class Test302 Relational operator
  {
  static void Main(string[] args) {
  int a = 20; int b = 20; int c = 30;
  Console.WriteLine(a == b);//true
  Console.WriteLine(a != b);//false
  Console.WriteLine(a > b);//false
  Console.WriteLine(a > c);//false
  Console.WriteLine(c > b);//true
  Console.WriteLine(a < c);//true
  Console.WriteLine(a >= c);//false
  Console.WriteLine(a <= c);//true
  }
  }}

3、 ... and . Logical operators
&& || !
1
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;/**

• Logical operators
• &&( And ): Both sides of the symbol hold at the same time be establish
• ||( or ): As long as one is established be establish
• !( Not ): The result is the opposite
  **/namespace Csp Personal course preparation . Chapter 3 operators and expressions {
  class Test303 Logical operators
  {
  static void Main(string[] args) {
  bool a = true;
  bool b = false;
  bool c = true;
  Console.WriteLine(a && b);//false
  Console.WriteLine(b || c);//true
  Console.WriteLine(!c);//false
  int d = 1;
  int e = 2;
  int f = 3;
  Console.WriteLine(d > e && f < e);//false
  Console.WriteLine(e < f || d > f);//true
  Console.WriteLine(!(f > d));//false
  }
  }}

Four . Assignment operator
( assignment ) += -= = /= %=
1
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;/*

• Assignment operator
• = += -= *= /= %=
  **/namespace Csp Personal course preparation . Chapter 3 operators and expressions {
  class Test304 Assignment operator
  {
  static void Main(string[] args) {
  int a = 10;
  int b = 20;
  int c;
  c = a + b;
  Console.WriteLine;//30
  c += a;
  Console.WriteLine;//40
  c -= a;
  Console.WriteLine;//30
  c /= 1;
  Console.WriteLine;//30
  b %= 2;
  Console.WriteLine(b);//0
  }
  }}

5、 ... and . An operation
&( Bitwise AND ) |( or ) ^( Exclusive or ) ~( Not ) <<( Move left ) >>( Move right )
1
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;/**

• An operator

•  &( Bitwise AND )	   |( or )		^( Exclusive or )	~( Not )   <<( Move left )	>>( Move right )	 >>>( unsigned right shift )
  

•   Binary system 
  

•  	 Decimal conversion binary 
  

•  13	 Binary system 	1101
  

•  2048	1024	512	  256	128	 64	 32	  16   8  4  2  1  Weighted power 
  

•  											   1  1  0  1
  

•  154							1     0   0    1   1  0  1  0
  

•  685				1       0   1     0   1    0   1  1  0  1
  

•  1250	1       0       0   1     1   1    0   0  0  1  0
  

•  243                         1     1   1    1   0  0  1  1
  

•  684             1       0   1     0   1    0   1  1  0  0
  

•  60                                    1    1   1  1  0  0
  

•  // Such as 243 You can reduce 128 What you can use is 1 The remainder can be reduced by further subtraction 1, Not enough minus is 0
  

•   Sign bit   1 It's a negative number    0  representative   Positive numbers 
  

**/namespace Csp Personal course preparation . Chapter 3 operators and expressions {
class Test305 An operator
{
static void Main(string[] args) {
int a = 60;
// Binary system :111100
int b = 13;// Binary system :001101 1101 Ahead 0 It was made up Positive complement 0 Negative numbers make up 1 In order to be consistent with the binary digits to be compared
int c = 0; //
c = a & b; // Binary system :001100 The corresponding bits are 1 The result is 1
Console.WriteLine;//12

		c = a | b;// Binary system :111101 As long as there is one corresponding to 1 The result is 1 	111101
		Console.WriteLine(c);//61

		c = a ^ b;// Binary system :110001 Corresponding bit   Same as 0  Different for 1
		Console.WriteLine(c);//49

		c = ~a;   // Binary system :000011  Corresponding bit    Take the opposite 
		Console.WriteLine(c);//-61

		c = a << 2; // Binary system :11110000
		Console.WriteLine(c);//240

		c = -a >> 60;// Binary system : Binary system  32 individual 1
		Console.WriteLine(c);//-1
	}
}}

6、 ... and . Conditional operator
( Ternary operator ) expression 1? expression 2: expression 3 -> 3>2?3:2
1
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;/**

• Ternary operator If otherwise

•  1? 2: 3
  

•  1: Conditions 	2: What to do if the conditions are met 	3. What to do if the condition is not established **/namespace Csp Personal course preparation . Chapter 3 operators and expressions {
  

  class Test306 Ternary operator
  {
  static void Main(string[] args) {
  int a = 10;
  int b;
  b = (a > 10) ? 100 : 50; // If a Greater than 10 Conditions be Established as 100, otherwise by 50.
  Console.WriteLine(b);// The condition doesn't hold, so 50
  }
  }}