[Diggory Laycock]

Hi here,

I really don't understand the syntax of the following line of code (from Apple's OutlineView sample code.)

I tried to search on Google for the answer - but the question mark makes this difficult.

I would also look this up in my copy of "A Book on C" but It's in London and I'm not!

Apologies for asking such an obvious question!

<BLOCKQUOTE><font size="1"face="Geneva, Verdana, Arial">code:</font><HR><pre><font size=1 face=courier>
- (int)outlineView NSOutlineView *)outlineView numberOfChildrenOfItem id)item {
return (item == nil) ? <font color = blue>1</font> : [item numberOfChildren];
} </font>[/code]

It's the ?1: part that I don't understand. What does it mean?

[Wixar]

The ? : operator is the one and only trinary operator in C. Its syntax is:

exp1 ? exp2 : exp3

First exp1 is evaluated. If it evaluates to true, then exp2 is evaluated, and the result of the entire expression is the value of exp2. Otherwise, exp3 is evaluated, and the result of the entire expression is exp3. Note that exp2 and exp3 must have the same type, and the type of the entire expression is that type.

So for the expression

(item == nil) ? 1 : [item numberOfChildren]

If item==nil evaluates to true (i.e. item is nil), then the expression evaluates to 1, and 1 is returned. Otherwise, the expression evaluates to [item numberOfChildren].

Any book on C should cover this; you would be well served by finding one.

-Peter

[Diggory Laycock]

Thanks very much. very helpful.