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

Question

What does this line of code mean?

label.frame = (inPseudoEditMode) ? kLabelIndentedRect : kLabelRect;

The ? and :

Answer 1

Ternary operator example.If the value of isFemale boolean variable is YES, print "GENDER IS FEMALE" otherwise "GENDER IS MALE"

? means = execute the codes before the : if the condition is true. 
: means = execute the codes after the : if the condition is false.

Objective-C

BOOL isFemale = YES;
NSString *valueToPrint = (isFemale == YES) ? @"GENDER IS FEMALE" : @"GENDER IS MALE";
NSLog(valueToPrint); //Result will be "GENDER IS FEMALE" because the value of isFemale was set to YES.

For Swift

let isFemale = false
let valueToPrint:String = (isFemale == true) ? "GENDER IS FEMALE" : "GENDER IS MALE"
print(valueToPrint) //Result will be  "GENDER IS MALE" because the isFemale value was set to false.

Answer 2

This is the C ternary operator (Objective-C is a superset of C):

label.frame = (inPseudoEditMode) ? kLabelIndentedRect : kLabelRect;

is semantically equivalent to

if(inPseudoEditMode) {
 label.frame = kLabelIndentedRect;
} else {
 label.frame = kLabelRect;
}

The ternary with no first element (e.g. variable ?: anotherVariable) means the same as (valOrVar != 0) ? valOrVar : anotherValOrVar

Answer 3

Simply, the logic would be

(condition) ? {code for YES} : {code for NO}

Answer 4

It's just a short form of writing an if-then-else statement. It means the same as the following code:

if(inPseudoEditMode)
  label.frame = kLabelIndentedRect;
else
  label.frame = kLabelRect;

Answer 5

It's the ternary or conditional operator. It's basic form is:

condition ? valueIfTrue : valueIfFalse

Where the values will only be evaluated if they are chosen.

Answer 6

This is part of C, so it's not Objective-C specific. Here's a translation into an if statement:

if (inPseudoEditMode)
    label.frame = kLabelIndentedRec;
else
    label.frame = kLabelRect;