int? a = null;
int? b = a * 5; //b = null 
int? c = a + 5; //c = null 

int? a = null;
int? b = null;
if (a > b)
{
 Console.WriteLine("a > b is true");
}
else
{
 Console.WriteLine("a > b is false");
}
if (a == b)
{
 Console.WriteLine("a == b is true");
}
else
{
 Console.WriteLine("a == b is false");
}

a > b is false
a == b is true

int? a = null;
int b = -5;
if (a >= b)
{
 Console.WriteLine("a>=b");
}
else
{
 Console.WriteLine("a<b");
}
if (a <= b)
{
 Console.WriteLine("a<=b");
}
else
{
 Console.WriteLine("a>b");
}

a<b
a>b