NULLABLE TYPES

Nullable types are instances of the System.Nullable struct. A nullable type can represent the normal range of values for its underlying value type, plus an additional null value. For example, a Nullable, pronounced “Nullable of Int32,” can be assigned any value from -2147483648 to 2147483647, or it can be assigned the null value. A Nullable can be assigned the values true or false, or null.
The ability to assign null to numeric and Boolean types is particularly useful when dealing with databases and other data types containing elements that may not be assigned a value. For example, a Boolean field in a database can store the values true or false, or it may be undefined.

int? i = 10;
double? d1 = 3.14;
bool? flag = null;
char? letter = 'a';
int?[] arr = new int?[10];