in C#? What are the uses

In C#? Represents a nullable type, which can represent all T values ​​of the base type and additional null values,? ? It means that the null coalescing operator means that when the operand is not null, it returns the value on the left side, otherwise it returns the right side, etc.

In C#? There will be different usages depending on the number, such as? and? ? The meanings of these two operators are different. Next, I will introduce the ? in C# to you in detail in the article. What are the specific usages? It has certain reference value. I hope it will be helpful to everyone.

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? (Nullable type)

A nullable type is an instance of the System.Nullable <T> structure. A nullable type can represent all values ​​T of the base type, as well as other NULL value. The underlying type T can be any non-nullable value type. But T cannot be a reference type.

Nullable types can be used when used to represent undefined values ​​of the underlying type. Nullable types have the following characteristics:

(1) Under a nullable type, a variable can be assigned a null value without creating a nullable type based on a reference type.

(2) Nullable types do not support nested Nullable types.

(3) Nullable types do not support var type. If Nullable and var are used, a compilation error will occur

Example:

// C# program to illustrate the 
// use of Nullable type 
using System; 
class GFG { 
    // 主方法
    static public void Main() 
    { 
        int ? a = null; 
        int ? b = 2345; 
        Console.WriteLine(a); 
        Console.WriteLine(b); 
    } 
}

Output result: 2345

? ? (Null coalescing operator)

In C#, the ?? operator is called the null-coalescing operator, which is the null coalescing operator. The meaning is that when the operand is not null, it returns the left operand; otherwise it returns the right operand. If you assign a nullable value type to a non-nullable value type without using the ?? operator, a compile-time error is generated. If a cast is used and no nullable value type is currently defined, an InvalidOperationException exception is thrown.

Example:

//声明a和b
int?a=null; 
int b;
b=a??2;//b的值为2
a=6;
b=a??8;//b的值为6

?: (ternary operator)

In C#, there is a special operator called ternary operation symbol, similar to if-else. The ternary operator compares two values ​​and returns a value based on it. The syntax of the ternary operator is:

条件表达式？表达式1：表达式2；

It can return a value of any data type.

Example:

using System;    
namespace Tutpoint  {      
class Program      
{          
public static void Compare(int a, int b)          
{              
string output = a > b ? "A 大于 B" : "B 大于 A";              
Console.WriteLine(output);          
}          
static void Main(string[] args)          
{             
 Program.Compare(66, 579);              
 Console.ReadKey();          
 }      
 }  }

The result output is: B is greater than A

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