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What does the two question marks together (??) mean in C#?
It is the null-coalescing operator. The null-coalescing operator ?? returns the value of its left-hand operand if it isn't null; otherwise, it evaluates the right-hand operand and returns its result. The ?? operator doesn't evaluate its right-hand operand if the lefthand operand evaluates to non-null.
A nullable type can represent a value that can be undefined or from the type's domain. We can use the ?? operator to return an appropriate value when the left operand has a nullable type. If we try to assign a nullable value type to a non-nullable value type without using the ?? operator, we will get a compile-time error and if we forcefully cast it, an InvalidOperationException exception will be thrown.
The following are the advantages of the Null-Coalescing Operator (??) operator −
It is used to define a default value for a nullable item (for both value types and reference types).
It prevents the runtime InvalidOperationException exception.
It helps us to remove many redundant "if" conditions.
It works for both reference types and value types.
The code becomes well-organized and readable.
Example
using System;
namespace MyApplication{
class Program{
static void Main(string[] args){
int? value1 = null;
int value2 = value1 ?? 99;
Console.WriteLine("Value2: " + value2);
string testString = "Null Coalescing";
string resultString = testString ?? "Original string is null";
Console.WriteLine("The value of result message is: " + resultString);
}
}
}Output
The output of the above example is as follows.
Value2: 99 The value of result message is: Null Coalescing
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