Use of question mark ? when setting a variable

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What does the question mark and the colon (?: ternary operator) mean in objective-c?

I understand that we're setting oldRow equal to some index path. I have never seen this syntax and can't find explanation in the book I'm using. What is the purpose of the ? in the code below and what exactly does this code do?

int oldRow = (lastIndexPath != nil) ? [lastIndexPath row] : -1;

max_ · Accepted Answer · 2012-06-14T18:57:56.447

7

int oldRow = (lastIndexPath != nil) ? [lastIndexPath row] : -1;

is equivalent to:

int oldrow = 0;
if (lastIndexPath != nil)
    oldRow = [lastIndexPath row];
else 
    oldRow = -1;

That syntax is called a ternary operator and follows this syntax:

condition ? trueValue : falseValue;

i.e oldRow = (if lastIndexPath is not nil ? do this : if it isn't do this);

edited Jun 14 '12 at 18:57

answered Jun 14 '12 at 17:44

max_

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Awesome. Thanks a lot. I see this syntax popping up a lot recently, so this was really helpful. – Sean Smyth Jun 14 '12 at 17:48
1

FWIW the correct name is ternary, not tertiary. – vcsjones Jun 14 '12 at 17:49
@vcsjones thanks, I have changed it. – max_ Jun 14 '12 at 18:58

score 2 · Answer 2 · answered Jun 14 '12 at 17:44

2

This is a shorthand if statement. Basically it is the same as:

int oldRow;

if(lastIndexPath != nil)
{
    oldRow = [lastIndexPath row];
}
else
{
     oldRow = -1;
}

It is very handy with conditional assignments

answered Jun 14 '12 at 17:44

rooster117

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score 1 · Answer 3 · answered Jun 14 '12 at 17:44

1

this code is equal to this code

int oldRow;

if (lastIndexPath != nil)
   oldRow = [lastIndexPaht row];
else
   oldRow = -1;

answered Jun 14 '12 at 17:44

Omar Abdelhafith

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Use of question mark ? when setting a variable

3 Answers3