When we compare value types with ==, the C# compiler performs a value comparison. For example, this prints true because the value 6 is equal to the value 6:

int int1 = 6;
int int2 = 6;
Console.WriteLine(int1 == int2);
// Output: true

int1 and int2 are the actual value 6. When we compare the value 6 with 6, they’re the same!

When we compare reference types with ==, the C# compiler performs a referential comparison, which means it checks if two variables refer to the same memory location. For example, this prints false because d1 and d2 refer to two different locations in memory (even though they contain objects with the same values):

Dissertation d1 = new Dissertation(50);
Dissertation d2 = new Dissertation(50);
Console.WriteLine(d1 == d2);
// Output: false

We constructed two different Dissertation objects which happened to have the same values. Each reference (d1 and d2) point to different objects, so they are not equal.