LinkedIn skill assessment answers and questions — Objective-C

“Objective-C is a powerful object-oriented programming language that forms the foundation of iOS app development. In this comprehensive guide, we’re excited to present a series of skill assessment questions and answers specifically tailored for Objective-C.

Whether you’re a seasoned developer looking to expand your capabilities or a beginner aiming to understand the basics of this powerful language, this resource is designed to help you become a master of Objective-C and its applications. Join us as we explore the fundamentals of Objective-C, memory management, delegation patterns, and other critical aspects of working with this cutting-edge language.”

Q1. What is the value of s?

NSMutableString *s = [NSMutableString stringWithString: @"123"];
[s appendString: @"456"];

•  123456
•  123
•  123
•  456
•  This code contains an error.

Q2. What’s the value of i after these statements?

NSString *str = nil;
NSInteger i = str.integerValue;

•  nil
•  0 (technically nil == 0 but i will have a literal value of 0 and not the void* value of nil)
•  -1
•  This code crashes.

Q3. What value is in str after this line in executed?

NSString str = "test" + " " + "more";

•  This code contains an error
•  test
•  nil
•  test more

Q4. What is the output of the code given below?

    NSPredicate *p2 = [NSPredicate predicateWithBlock:^BOOL(NSString*  evaluatedObject, NSDictionary<NSString *,id> * _Nullable bindings) {
      return evaluatedObject.intValue % 2 == 0;
    }];
    NSArray *vals = @[@"1", @"2", @"3"];
    NSArray *n2 = [vals filteredArrayUsingPredicate:p2];
    NSLog(@"%@", n2.firstObject);

•  2
•  1,2,3
•  1,2
•  Nothing, since this code contains an error.

Q5. Property defaults include _?

•  atomic/strong
•  atomic/weak
•  nonatomic/weak
•  nonatomic/strong

Q6. What is the key difference between NSDictionary and NSMutableDictionary?

•  NSMutableDictionary’s values can change
•  NSMutableDictionary has not initializers.
•  NSDictionary can’t be copied.
•  NSDictionary’s values can change.

Q7. What is foo?

-(float)foo;

•  A function with a return type of float.
•  This code contains an error.
•  A variable declaration of type float.
•  A property of type float.

Q8. What can you glean from this line?

#import "NSString+NameHelper.h"

•  NameHelper is a category of NSString.
•  NameHelper is a subclass of NSString.
•  NSString implements the NameHelper protocol.
•  NSString has a helper class.

Q9. What’s wrong with this code?

float x = 5.;

•  Nothing is wrong with this code.
•  Declarations do not need semicolons.
•  x=5 is an invalid float.
•  Variables can’t be declared and initialized in the same state.

Q10. How many times with this loop be executed?

for (int x=0; x<100; x++) {
  x = x + 1;
}

•  50
•  99
•  100
•  This code contains an error.

Q11. What is this code an example of?

[self addObserver: self forKeyPath: @"val" options:0 context: nil];

•  Key-Value Observing
•  Class Value Observing
•  Key-Data Observing
•  KeyPath Observing

Q12. What does ARC stand for?

•  Automatic Reference Counting
•  Automatic Retain Checking
•  Async Retain Cycles
•  Automatic Release Code

Q13. What is printed for this code?

int val = 0;
val = 1.5;
printf("%d", val);

•  1
•  2
•  0
•  This code contains an error.

Q14. What best describes class inheritance in Objective-C?

•  single inheritance but multiple protocol implementation
•  Objective-C doesn’t support inheritance
•  dual class inheritance
•  unlimited class inheritance and protocol adherence

Q15. How many keys does this NSDictionary have after this code is executed?

NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys: @"b", @"e", @"a", @"r", nil];

•  2
•  4
•  5
•  This code contains an error.

Q16. What is the error in this code?

NSMutableDictionary *dict1 = [NSMutableDictionary dictionaryWithCapacity:5];
[dict1 setValue:@"key" forKey:@"value"];

•  The key and value items are mixed
•  Nothing is wrong with it
•  You can’t set the capacity of a dictionary
•  NSMutableDictionary doesn’t have a :setValue:forKey function.

Q17. What is printed from this code?

NSData *data = [@"print" dataUsingEncoding:NSASCIIStringEncoding];
NSLog(@"%@", [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding]);

•  print
•  This code is invalid
•  Nothing is printed from this code.
•  nil

Q18. What is different about this function?

+(void)doSomething;

•  It is static
•  It is abstract.
•  It is inline.
•  This code contains an error.

Q19. Structs can have _?

•  functions
•  initializers
•  fields
•  all of these answers

Q20. What is wrong with this code?

@interface MyClass : NSObject
    @property (strong, nonatomic, readonly) NSString *name;
  @end

•  There is nothing wrong with this code.
•  There is not read-only directive.
•  MyClass doesn’t implement NSObject.
•  Properties are declared in the implementation.

Q21. What is an enums base type for the code below?

typedef enum { Foo1, Foo2} Foo;

•  There is no base type.
•  NSObject
•  int
•  NSNumber

Q22. If you want to store a small amount of information (e.g., user settings), whats the best, built-in way to go?

•  UserDefaults
•  plist file
•  CoreData
•  TextFile

Q23. What are categories used for?

•  to extend other classes
•  to manage access control
•  to coordinate objects
•  to group classes

Q24. What is this Objective-C code checking?

if ([keyPath isInstanceOf:[NSString class]]) {
}

•  This code contains an error
•  if keyPath is an instance of NSString
•  if keyPath’s baseclass is the same as NSString’s baseclass
•  if keyPath implements the same methods as NSString

Q25. What is this a declaration of?

int(^foo)(int);

•  an Extension
•  a Generic
•  a block of code
•  an abstract class

Q26. For observing changes to a property, which of these two statements cause the related method to be called and why?

1. _val = 1;
2. self.val= 100;

•  Statement 2, since it calls the auto-created setter on the property.
•  Statement 1, since it uses the property directly.
•  Statement 2, since it specifies the class instance to use.
•  Statement 1, since it calls the auto-created setter on the property.

Q27. What is wrong with this code?

float x = 2.0;
int(^foo)(int) = ^(int n1) {
  return (int)(n1*x);
};
foo(5);

•  Ints and floats can’t be multiplied.
•  The parameter isn’t declared correctly.
•  x is not in the right scope.
•  Nothing is wrong with this code.

Q28. What’s the difference between an array and a set?

•  Arrays are ordered, non-unique values.
•  Arrays are stored sorted.
•  Sets are ordered, unique values.
•  Sets can contain nils.

Q29. Dot notation can be used for _?

•  nothing, as they’re never used in Objective-C
•  function calls only
•  property getter/setter
•  parameter delimiters

Q30. What is the value of newVals after this code is executed?

NSArray *vals = @[@"1", @"2", @"3"];
NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF.intValue > 1"];
NSArray *newVals = [vals filteredArrayUsingPredicate:pred];

•  2,3
•  nil
•  This code contains an error
•  2,”3″

Q31. How would this function be called?

-(int)foo:(int)a b:(int)c;

•  self.foo(5, b:10);
•  This code contains an error.
•  [self foo:5:10:20];
•  [self foo:5 b:10];

Q32. What is the type of the error return value stored in json?

NSError *error;
NSData *data;
id json = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];

•  NSString
•  NSArray
•  id
•  NSDictionary

Q33. What is significant about this function declaration?

-(void)testFunc:(NSString**)str;

•  The parameter is passed by value and can not be changed
•  ** is not allowed on a parameter
•  The parameter may be nil
•  The parameter is passed by reference and may be changed

Q34. What is printed from this code execution?

typedef enum {
    thing1,
    thing2,
    thing3
} Thing;


-(void) enumStuff {
    NSLog(@"%d", thing2);
}

•  0
•  1
•  thing2
•  This code does not print anything

Q35. You are worried about threaded access to a property and possible collision in writing. What directive should you use on the property?

•  non-atomic
•  strong
•  weak
•  atomic

Q36. What is wrong with this line of code?

int temp = 1==1;

•  temp is a keyword.
•  1==1 is invalid.
•  1==1 evaluates to a Boolean.
•  Nothing is wrong with it.

Q37. What is special about the code within this block?

dispatch_async(dispatch_get_main_queue(), ^{
// code
});

•  It executes on the main queue.
•  It is the last code to run before the app goes inactive.
•  It executes on a background thread.
•  It is queued to execute in the background.

Q38. How many items are in set1 after this code executes?

NSMutableSet *set1 = [NSMutableSet setWithObjects: @1,@2, @3, @4, @5, nil];
[set1 add0bject:@3];

•  zero
•  six
•  one
•  five

Q39. What is wrong with this code?

NSDictionary *d1 = @[@"v1", @4, @"v2", @5.6, @"v3"];
NSlog(@"d1: %@", d1);

•  NSDictionary cannot be printed this way.
•  The last key is missing a value.
•  Dictionaries cannot have mixed types as values.
•  d1 is assigned an NSArray of values.

Q40. What is the initial value of the property val?

@property (nonatomic, readonly) int val;

•  8
•  nil
•  -1
•  undefined

Q41. Which thread should UI updates be processed on to avoid crashes and application lag?

•  UI
•  dispatch
•  background
•  main

Q42. What is the value of val after this code is executed?

NSString *val = @"1.23";
BOOL tf = val.boolValue;

•  This code is invalid
•  YES
•  NO
•  1

Q43. In this code, what does ThatOne refer to?

@interface TestClass : ThisOne <ThatOne>

•  the parent class of TestClass
•  the name of the category being created for ThisOne
•  a protocoL impLemented by ThisOne
•  a helper file’s name

Q44. What is the value of result after this code is executed?

NSString *result = [Ftest"
    stringByTrimmingCharactersInSet.NSCharacterSet.alphanumericCharacterSet];

•  “”
•  “es”
•  “test”
•  none of these answers

Q45. When will self receive the notification based on this code?

MyClass .classObj = [[MyClass allot] init];
[class0bj add0bserver:self forKeyPath:@"name"
              options:NSKeyValueObservingOptionNew context:NULL];

•  none of these answers
•  class0bj will recieve the notification, not self.
•  when class0bj is set to “name”
•  when the name property in the class0bj instance changes

Q46. What is wrong with this code?

[*"true" boolValue];

•  String literal are not created with*.
•  NSString doesn’t have a boolValue function.
•  “true” has no meaning.
•  There is nothing wrong with this code.

Q47. How many times does this loop execute?

int loopVal = 0;
for (int i=0; i>loopVal; i--){
    i--;
}

•  an infinite number of times
•  This code is invalid.
•  zero
•  one

Q48. What will this code print?

NSLog(@"%lu", @"test".length);

•  “test”
•  Nothing, this code is invalid.
•  4
•  0

Q49. What is the value of numVtoInt after this code is executed?

NSNumber *numV = [NSNumber numberWithFloat:6.7];
int numVtoInt = numV.intValue;

•  6
•  0
•  6.7
•  7

Q50. What does this code print?

NSString *val = @"1.23";
NSLog(@"%.04f", val.floatValue);

•  1.2300
•  .04
•  This code is invalid
•  1

Q51. What is the maximum possible value of r1 in this code?

int r1 = arc4random() % 10;

•  0
•  9
•  1
•  10