Check out example codes for "c# double question mark". It will help you in understanding the concepts better.

Code Example 1

int? a = null;
int b = a ?? -1;		// Same as b = ( a != null ? a : -1 );
Console.WriteLine(b);  	// output: -1
//OR IF
int? a = 9;
int b = a ?? -1;
Console.WriteLine(b);  	// output: 9

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