?? and ??= Null coalescence operators C#

 C# introduces the ?? and ??= operators which are known as the Null coalescence operators.

Purpose -
The ?? and ??= operators can help in cases where a comparison is made between two or more variable values and depending on the order in the statement, the variable valu is used.

Say for example there is variable either a and b to be returned by a method. Say if value is needed to be returned if it is not null and if yes, the value b is supposed to be returned.

```
public class NullCoal
{
public static int? Method(int? input)
{
    ....
    ....
    int? a;
    int? b;
    

    if(input > 10)
    {
        a = input * 6;
    }
    else
    {
        b = input * 7:;
    }

    return a ?? b;
}
}

```
In the above example, a is returned if it is not null or b is returned.

Similarly the ??= operator adds the assignment operation as well, which can be used like

```
    int? a = null;
    int? b = 1;

    a ??= b;
```
where if a is not null, value of b is assigned to it, otherwise nothing happens with the above statement.

The null coalescence operator is a short form for writing the below code.

```
if( a is null)
{
    a = 1;
}

```
instead it can be written as

```
a ??= 1;
```
What if there is more than two variables to check, in such cases say like below
```
return a ?? b ?? c;
```
the expression is evaluated from right to left like this
```
return a ?? ( b ?? c)
```