Question

I often do this when necessary to prevent a null pointer exception:

// Example #1
if (cats != null && cats.Count > 0)
{
  // Do something
}

In #1, I’ve always just assumed that the cats != null needs to be first, because order of operations evaluate from left to right.

However, unlike example #1, now I want to do something if the object is null or if the Count is zero, therefore I’m using logical OR instead of AND:

// Example #2
if (table == null || table.Rows == null || table.Rows.Count <= 0)
{
  // Do something
}

Does the order of the logical comparisons matter? Or can I also reverse the order and get the same results, such as in Example #3?

// Example #3
if (table.Rows.Count <= 0 || table.Rows == null || table == null)
{
  // Do something
}

(btw, I realize I can rewrite #2 like below, but I think it’s messy, and I’m still curious about the OR operators)

// Example #4
if (!(table != null && table.Rows != null && table.Rows.Count > 0))
{
  // Do something
}

Answer 1

Yes, the short-circuiting happens in both cases, the only difference being that && stops if the LHS is false (because the overall expression must then be false) while || stops if the LHS is true (because the overall expression must be true).

The first two examples in your question are correct, the third will throw an exception if table or table.Rows are null.