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   confuse me

User · Answer

Simply  the logic would be   condition     code for YES     code for NO

User · Answer

That s just the usual ternary operator   If the part before the question mark is true  it evaluates and returns the part before the colon  otherwise it evaluates and returns the part after the colon   a b c   is like  if a      b  else     c

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Fun fact  in objective-c if you want to check null   nil For example   - NSString   getSomeStringSafeCheck       NSString  string    self getSomeString       if string    nil           return String            return          The quick way to do it is   - NSString   getSomeStringSafeCheck       return  self getSomeString     nil    self getSomeString             Then you can update it to a simplest way   - NSString   getSomeStringSafeCheck       return  self getSomeString             Because in Objective-C    if an object is nil  it will return false as boolean  Ternary Operator s second parameter can be empty  as it will return the result on the left of       So let say you write    self getSomeString     nil          the second parameter is returning a boolean value  thus a exception is thrown

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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

User · Answer

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

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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

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int padding      UIScreen mainScreen  bounds  size height  lt   480    15   55    means  int padding   if    UIScreen mainScreen  bounds  size height  lt   480    padding   15  else   padding   55

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It is ternary operator  like an if else statement   if a  gt  b    what to do    else   what to do      In ternary operator it is like that   condition   what to do if condition is true   what to do if it is false    a  gt  b    what to do if true   what to do if false

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I just learned something new about the ternary operator  The short form that omits the middle operand is truly elegant  and is one of the many reasons that C remains relevant  FYI  I first really got my head around this in the context of a routine implemented in C   which also supports the ternary operator  Since the ternary operator is in C  it stands to reason that it would be in other languages that are essentially extensions thereof  e  g   Objective-C  C

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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

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As everyone referred that  It is a way of representing conditional operator  if  condition        true     else       false     using ternary operator  condition   true false To add additional information  In swift we have new way of representing it using      let imageObject  UIImage    UIImage named   ImageName        initialOfUsername capitalizedString  imageFromString   Which is similar to   int a   6  c  5  if  a  gt  c       a is greater   else    c is greater     is equivalent to   if  a gt c  a c     Is equal to if  a gt c   c  instead of    we can use    is swift

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Building on Barry Wark s excellent explanation     What is so important about the ternary operator is that it can be used in places that an if-else cannot  ie  Inside a condition or method parameter    NSString stringWithFormat    Status        statusBool     Approved      Rejected         which is a great use for preprocessor constants      in your pch file     define statusString  statusBool     Approved      Rejected       in your m file     NSString stringWithFormat    Status       statusString    This saves you from having to use and release local variables in if-else patterns  FTW

User · Answer

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

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

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