Objective-C Skill Assessment Quiz

Table of Contents

Objective-C Skill Assessment Quiz | Test Your Knowledge | Objective-C is a high-level general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was selected by NeXT for its NeXTSTEP operating system.

Q1. What is the value of s?

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

123456
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 does this code print?

    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"

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 wrong with 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.

Objective-C