The basic grammatical structure of C language

C# The basic grammatical structure of language

The knowledge structure ：

---

1、 data type

The first category ：

• Simple data type ：byte、short、int、long、float、double、char、bool
• Combined data types ：struct、enum、class、interface

type	describe
byte	Unsigned 8 An integer
(ushort) short	（ nothing ） A signed 16 An integer
(uint) int	（ nothing ） A signed 32 An integer
(ulong) long	（ nothing ） A signed 64 An integer
float	32 Bit floating point type
double	64 Bit floating point type
char	16 position unicode character （ International standard character set ）
bool	Boolean type

The second category ：

• Value type ： When passed as a parameter , Deliver copy .
  • Include ： Simple data type 、struct type 、enum type
• Reference type ： When passed as a parameter , Delivery address .
  • Include ：class type 、 Array

example 1：

public struct Book
{
    
    public double Price;
    public string Title;
    public string Author;
}

class Program
{
    
    static void ChangeBook(Book bk)
    {
    
        bk.Price = 1.01;
        bk.Title = "Spss";
        bk.Author = "John";
    }

    static void PrintBook(Book bk)
    {
    
        Console.WriteLine("Book Infor:\n Price={0},Title={1},Author={2}",
            bk.Price, bk.Title, bk.Author);
    }
    static void Main(string[] args)
    {
    
        Book bk;// = new Book();
        bk.Price = 10.01;
        bk.Title = "MatLab";
        bk.Author = "Tom";
        PrintBook(bk);
        ChangeBook(bk);
        PrintBook(bk);

        //Book Infor:
        //Price=10.01,Tile=MatLab,Author=Tom
        //Book Infor:
        //Price=10.01,Tile=MatLab,Author=Tom
    }
}

This example shows “ Value type ” Deliver copy , Do not change the value stored by itself .

example 2：

public class Book
{
    
    public double Price;
    public string Title;
    public string Author;
}

class Program
{
    
    static void ChangeBook(Book bk)
    {
    
        bk.Price = 1.01;
        bk.Title = "Spss";
        bk.Author = "John";
    }

    static void PrintBook(Book bk)
    {
    
        Console.WriteLine("Book Infor:\n Price={0}, Tile={1}, Author={2}",
            bk.Price, bk.Title, bk.Author);
    }

    static void Main(string[] args)
    {
    
        Book bk = new Book(); // error  Book bk;
        bk.Price = 10.01;
        bk.Title = "MatLab";
        bk.Author = "Tom";
        PrintBook(bk);
        // Book Infor:
        // Price = 10.01, Tile = MatLab, Author = Tom
        
        ChangeBook(bk);
        PrintBook(bk);
        // Book Infor:
        // Price = 1.01, Tile = Spss, Author = John
    }
}

example 3：

class Program
{
    
    static void ChangeArrayItem(int[] array)
    {
    
        for (int i = array.Length - 1; i >= 0; i--)
        {
    
            array[i] = array.Length - 1 - i;
        }
    }
    static void PrintArrayItem(int[] arry)
    {
    
        for (int i = 0; i < arry.Length; i++)
        {
    
            Console.Write("{0} ", arry[i]);
        }
        Console.WriteLine();
    }

    static void Main(string[] args)
    {
    
        int[] arr = new int[3];
        for (int i = 0; i < arr.Length; i++)
        {
    
            arr[i] = i;
        }
        PrintArrayItem(arr); // 0 1 2
        ChangeArrayItem(arr);
        PrintArrayItem(arr); // 2 1 0
    }
}

example 2, example 3 explain “ Reference type ” Delivery address , To change the value stored by itself . In specific application , it is to be noted that “ Value type ” and “ Reference type ” The difference between .

---

2、 Variables and constants

• Variable definitions ： Variable type Variable name ;
• Constant definition ：
  • readonly Initialize in a declaration or constructor
  • const Initialize on declaration

example 4：

public class SimpleClass
{
    
    public int X;
    public readonly int Y = 2;
    public readonly int Z;
    public const double Pi = 3.1415926;
    public const string Etc = "...";
    public SimpleClass()
    {
    
        Z = 3;
    }
    public SimpleClass(int p1, int p2, int p3)
    {
    
        X = p1;
        Y = p2;
        Z = p3;
    }
}

class Program
{
    
    static void Main(string[] args)
    {
    
        SimpleClass sp1 = new SimpleClass();
        sp1.X = 1;
        Console.WriteLine("sp1:x={0}, y={1}, z={2}", sp1.X, sp1.Y, sp1.Z);
        // sp1: x = 1, y = 2, z = 3

        SimpleClass sp2 = new SimpleClass(-1, -2, -3);
        Console.WriteLine("sp2:x={0} ,y={1}, z={2}", sp2.X, sp2.Y, sp2.Z);
        // sp2: x = -1 ,y = -2, z = -3

        Console.WriteLine("PI={0}{1}", SimpleClass.Pi, SimpleClass.Etc);
        // PI = 3.1415926...
    }
}

Attention to the above examples readonly And const Define a constant and the difference when using it .

---

3、 Operators and expressions

Operator ：

• Unary operator x++,y++
• Binary operator x+y,x-y
• Ternary operator max = (x>y)?x:y;

Operator ：

• Arithmetic operator +、-、*、/、%
• Relational operator >、>=、==、!=、<=、<
• Logical operators !、&&、||

expression ： An expression consisting of an operator and a variable or constant .

---

4、 Basic statement

4.1 Assignment statement

Variable name = expression ;

4.2 Conditional statements

The first one is ：

if( Conditional expression )
{
    
     Statement sequence ;
}

The second kind ：

if( Conditional expression )
{
    
     Statement sequence ;
}
else
{
    
     Statement sequence ;
}

The third kind of ：

if( Conditional expression 1)
{
    
     Statement sequence 1;
}
else if( Conditional expression 2)
{
    
     Statement sequence 2;
}
else if( Conditional expression N)
{
    
     Statement sequence N;
}
else
{
    
     Statement sequence N+1;
}

4.3 Switch statement

swith( expression )
{
    
    case  value 1： Statement sequence 1; break;
    case  value 2： Statement sequence 2; break;
    case  value N： Statement sequence N; break;
    default： Statement sequence N+1; break;
}

example 5：

class Program
{
    
    static void Main(string[] args)
    {
    
        Random rdm = new Random();
        int i = rdm.Next(1, 5);
        Console.WriteLine(i); // 1
        switch (i)
        {
    
            case 1:
                Console.WriteLine("Case 1.");
                break;
            case 2:
                Console.WriteLine("Case 2.");
                break;
            case 3:
                Console.WriteLine("Case 3.");
                break;
            default:
                Console.WriteLine("Default Case.");
                break;
        }
        // Case 1.

        i = rdm.Next(1, 5);// 1
        Console.WriteLine(i);
        switch (i)
        {
    
            case 1:
            case 2:
            case 3:
                Console.WriteLine("It's 1,2 or 3.");
                break;
            default:
                Console.WriteLine("Not Sure What it is.");
                break;
        }
        //It's 1,2 or 3.
    }
}

Attention to the above examples switch The grammatical structure of a sentence , Especially every one case Statements need to match break sentence .

4.4 Loop statement

The first one is ：

for( Initialize the loop counter expression ; Determine the end condition of the cycle ; Increment or decrement loop counter expression )
{
    
     Statement sequence ;
}

The second kind ：

while( Conditional expression )
{
    
     Statement sequence ;
}

The third kind of ：

do
{
    
     Statement sequence 
}while( Conditional expression );

A fourth ：

foreach( Element type   Elements  in  aggregate )
{
    
     Statement sequence ;// It is usually used to traverse every element in a collection 
}

example 6：

class Program
{
    
    static void Main(string[] args)
    {
    
        int i;
        int sum = 0;
        for (i = 1; i <= 10; i++)
        {
    
            sum += i;
        }
        Console.WriteLine(sum);// 55

        sum = 0;
        i = 1;
        while (i <= 10)
        {
    
            sum += i;
            i++;
        }
        Console.WriteLine(sum);// 55

        sum = 0;
        i = 1;
        do
        {
    
            sum += i;
            i++;
        } while (i <= 10);
        Console.WriteLine(sum);// 55
    }
}

example 7：

class Program
{
    
    static void Main(string[] args)
    {
    
        int[] arry = new int[] {
     1, 3, 5, 7 };
        foreach (int i in arry)
        {
    
            Console.WriteLine(i);
        }
        // 1
        // 3
        // 5
        // 7
    }
}

4.5 try…catch…finally sentence

try
{
    
     Statement sequence ;
}
catch(Exception ex)
{
    
     Statement sequence ;
}
finally
{
    
     Statement sequence ;
}

example 8： Enter an integer on the screen , Then the integer will be displayed on the screen “*” Number .

class Program
{
    
    static void Main(string[] args)
    {
    
        Console.WriteLine(" Please enter an integer :");
        //  Please enter an integer :
        // abc

        string sTemp = Console.ReadLine();
        try
        {
    
            int iCount = int.Parse(sTemp);
            for (int i = 0; i < iCount; i++)
            {
    
                Console.Write("*");
            }
            Console.WriteLine();
        }
        catch (Exception ex)
        {
    
            Console.WriteLine(" The reason for the mistake is :" + ex.Message);
            //  The reason for the mistake is : The input string is not in the correct format .
        }
        finally
        {
    
            Console.WriteLine(" end .");
            //  end .
        }
    }
}

Attention to the above examples try…catch…finally The grammatical structure of a sentence , This statement is usually used to catch and handle exceptions .

4.6 break、continue sentence

• break sentence ： Jump out of the innermost closed loop or switch In the sentence
• continue sentence ： Pass control to the next iteration of the closed loop

example 9：

class Program
{
    
    static void Main(string[] args)
    {
    
        for (int i = 1; i <= 100; i++)
        {
    
            if (i == 5)
                break;
            Console.WriteLine(i);
        }
        // 1
        // 2
        // 3
        // 4

        for (int i = 1; i <= 100; i++)
        {
    
            if (i < 99)
                continue;
            Console.WriteLine(i);
        }
        // 99
        // 100
    }
}

4.7 Comment statement

• Single-line comments ：// Text sequence
• Multiline comment ：/* Text sequence */