C# do you need to check if something has a value and if something is greater than 0?

The code is probably redundant.

If i is int? then:

if (i.HasValue && i.Value > 0)

is equivalent to:

if (i > 0)

From MSDN:

When you perform comparisons with nullable types, if the value of one of the nullable types is null and the other is not, all comparisons evaluate to false except for != (not equal). It is important not to assume that because a particular comparison returns false, the opposite case returns true. In the following example, 10 is not greater than, less than, nor equal to null. Only num1 != num2 evaluates to true.

It might be that the value for the variable has different meanings in that context.

int? someNumber = null; //might mean "there is no value"
int? someOtherNumber = 0; //might mean "the user has selected: 0"

The following:

class Program {
    static void Main(string[] args) {
        int? i = null;
        if (i > 0) { Console.WriteLine(">0");
        } else {     Console.WriteLine("not >0");
        }
        if (i < 0) { Console.WriteLine("<0");
        } else {     Console.WriteLine("not <0");
        }
        if (i == 0) {Console.WriteLine("==0");
        } else {     Console.WriteLine("not ==0");
        }
        Console.ReadKey();
    }
}

will output

not >0
not <0
not ==0

without throwing an exception. So the null/HasValue check in this case is redundant. There is one small difference. The following:

(i.HasValue && (i.Value == 0))

is about twice as fast as

(i == 0)

when i is null although both are so fast it's not an important difference. When i has a value, the two comparisons take about the same amount of time.