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Thread: Online C++ Test Questions

  1. #1
    Join Date
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    Online C++ Test Questions

    Hello Everyone, I recently gave an online C++ test. Below are few of the questions I need help with. Could anyone please explain to me the correct answers?

    1) Can we call virtual function from non-virtual function?
    2) Can we call pure virtual function from constructor?
    3) Benefits of Templates over overriding
    Code:
    i)	One copy of code in memory
    ii)	Fast
    4)
    Code:
    Obj1 = obj2 ........... points to the same memory location?
    5) Rough Code below
    Code:
    Class Object1; (no object created)
    Class Object2 obj2; (one object created)
    cout << dynamic_cast< Object1>(obj2) << endl; ....... prints what?
    6) How to find a substring in a map key(syntax?), the key stores a string.
    7) Returning an array from function (syntax of function signature?)
    8) Default copy constructor does what
    Code:
    i)	Reference to the original object of the same class
    ii)	Does nothing by default
    9) Assign const pointer to a non-const pointer
    Code:
    i)	Reinterpret
    ii)	Dynamic_cast
    iii)	Const_cast
    iv)	Static_cast
    10) If we do not write a constructor, the compiler generates one for us. Is there a default destructor too?
    11) How to print vector elements in a separate function having only a print statement
    Rough Code
    Code:
    For_each(syntax for iteratring, printFunc) – syntax?????
    For() {}  – syntax?????
    int printFunc(int i)
    {cout << i << endl;}
    12) What does double ( ## ) between two variables and single ( # ) before one variable in macros mean?
    e-g ...
    Code:
     {#xyz ## #jkl}
    13) Rough Code
    Code:
    Pointer1 ptr1 = new Pointer;
    Pointer2 ptr2;
    ptr2 = ptr1; ..... how to assign? Syntax

  2. #2
    Join Date
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    Posts
    27,418

    Re: Online C++ Test Questions

    Quote Originally Posted by gulHK View Post
    Hello Everyone, I recently gave an online C++ test. Below are few of the questions I need help with. Could anyone please explain to me the correct answers?
    First, let's see your answers.

    I know that some of the questions are worded badly, but others can be solved by just writing a simple program and testing your solution here:

    http://www.compileonline.com/compile_cpp_online.php

    Regards,

    Paul McKenzie

  3. #3
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    146

    Re: Online C++ Test Questions

    Hello Paul. Below are my answers.

    Thanks and Regards

    1) Can we call virtual function from non-virtual function? YES

    2) Can we call pure virtual function from constructor? NO (Read this answer somewhere but I don't know the reason)

    3) Benefits of Templates over overloading
    Code:
    i)	One copy of code in memory
    ii)	Fast (YES as it avoids pointers/polymorphism)
    4)
    Code:
    Obj1 = obj2 ........... points to the same memory location?
    5) Rough Code below
    Code:
    Class Object1; (no object created)
    Class Object2 obj2; (one object created)
    cout << dynamic_cast< Object1>(obj2) << endl; ....... prints what?
    6) How to find a substring in a map key(syntax?), the key stores a string.
    Code:
    I know how to find a key and then extract the substring from it but is there way to do it in one step? Because the choices I remember were all ONE LINE statements - e-g find_first_of
    7) Returning an array from function (syntax of function signature?)
    Code:
    int* foo(params) - We get a memory address pointing to the 0th element of the Array
    8) Default copy constructor does what
    Code:
    i)	Reference to the original object of the same class
    ii)	Does nothing by default ... FALSE b'coz then why would compiler provide one, I am still not sure of the exact reason
    9) Assign const pointer to a non-const pointer
    Code:
    i)	Reinterpret
    ii)	Dynamic_cast
    iii)	Const_cast (YES ... const_cast operator is used to add or remove a const or volatile modifier to or from a type)
    iv)	Static_cast
    10) If we do not write a constructor, the compiler generates one for us. Is there a default destructor too? (YES)
    11) How to print vector elements in a separate function having only a print statement
    Rough Code
    Code:
    For_each(syntax for iteratring, printFunc) – syntax?????
    For() {}  – syntax?????
    int printFunc(int i)
    {cout << i << endl;}
    12) What does double ( ## ) between two variables and single ( # ) before one variable in macros mean?
    e-g ...
    Code:
     {#xyz ## #jkl}
    13) Rough Code
    Code:
    Pointer1 ptr1 = new Pointer;
    Pointer2 ptr2;
    ptr2 = ptr1; ..... how to assign? Syntax
    Last edited by gulHK; September 19th, 2013 at 11:24 AM.

  4. #4
    Join Date
    Apr 1999
    Posts
    27,418

    Re: Online C++ Test Questions

    Quote Originally Posted by gulHK View Post
    Hello Paul. Below are my answers.

    Thanks and Regards

    1) Can we call virtual function from non-virtual function? YES
    OK. That's right.
    2) Can we call pure virtual function from constructor? NO (Read this answer somewhere but I don't know the reason)
    You can call a function, but the "virtualness" will not be exhibited in the constructor. When an object is constructed, any call to a virtual function will just invoke the function as if it is non-virtual.
    3) Benefits of Templates over overloading
    Code:
    i)	One copy of code in memory
    ii)	Fast (YES as it avoids pointers/polymorphism)
    The simple answer is that you can write one set of generic code, and "overload" the code on a compile-time type. You can't do that with regular overloaded functions.
    4) [code]Obj1 = obj2 ........... points to the same memory location?
    More information is needed. Of course if Obj1 and obj2 are pointers to a type T, then they will point to the same memory location. If Obj1 and obj2 are different objects, then they will be two distinct objects.
    5) Rough Code below
    [code]Class Object1; (no object created)
    Class Object2 obj2; (one object created)
    There is no such keyword in C++ as Class. So the question cannot be answered.
    7) Returning an array from function (syntax of function signature?)
    Code:
    int* foo(params) - We get a memory address pointing to the 0th element of the Array
    Don't know if this is a trick question. Your answer returns a pointer, not an array. Can you actually return an array in C++? I ask you.
    8) Default copy constructor does what
    Code:
    i)	Reference to the original object of the same class
    ii)	Does nothing by default ... FALSE b'coz then why would compiler provide one, I am still not sure of the exact reason
    You need to know this one, or you can be rejected by any interviewer right from the start.

    The default copy constructor does a member-wise, "shallow" copy on all the individual members of the class or struct.
    11) How to print vector elements in a separate function having only a print statement
    Well, this one uses a "std::copy", not "print", as there is no such function as "print" in standard C++.
    Code:
    #include <vector>
    #include <algorithm>
    #include <iostream>
    #include <iterator>
    //...
    template <typename T>
    void PrintVector(const std::vector<T>& tVect)
    {
        std::copy(tVect.begin(), tVect.end(), std::ostream_iterator<T>(std::cout, " "));
    }
    
    int main()
    {
        std::vector<int> IntVector;
        IntVector.push_back(10);
        IntVector.push_back(20);
        IntVector.push_back(30);
        IntVector.push_back(40);
        PrintVector(IntVector);
    }
    That's all I'll contribute for now.

    Regards,

    Paul McKenzie

  5. #5
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    Re: Online C++ Test Questions

    4) without knowing a whole lot more about obj1 and obj2, the question cannot be answered as the operator = could be overloaded.
    All advice is offered in good faith only. You are ultimately responsible for effects of your programs and the integrity of the machines they run on.

  6. #6
    GCDEF is offline Elite Member Power Poster
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    11,980

    Re: Online C++ Test Questions

    Quote Originally Posted by 2kaud View Post
    4) without knowing a whole lot more about obj1 and obj2, the question cannot be answered as the operator = could be overloaded.
    Or they could be pointers. The questions aren't worded well at all.

  7. #7
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    Re: Online C++ Test Questions

    Thank You Very Much Paul. Please have a look at the questions/answers below

    4)
    Code:
     Obj1 and Obj2 are the Objects of the same class (type)
    e-g if “Object” is the class name:
    Object obj1 = new Object(); 
    Object obj2;
    Obj2 = obj1 ........... do these objects point to the same memory location?
    5) Rough Code Below
    Code:
    Object1 and Object2 are the names of two different classes.
    The Class Object2 has one Object and the Class Object1 does not have any objects 
    Object2 obj2 = new Object2();
    cout << dynamic_cast< Object1>(obj2) << endl; ....... prints what?
    7) Returning an array from function syntax
    Code:
    int * foo(int arr[]) … this was one of the choices given
    What I learnt is that NO we cannot return an array but a pointer to the first element of the array
    Code:
    int * foo(int arr[]){
        // populate arr
        return arr;
    }
    
    int main()
    {
      int arrA [10];
      int *arrB = foo(arrA);
      for(int i=0; i<10; i++)
      {
      	cout << arrB[i] << endl;
      }
    }
    8) Default copy constructor does what
    Code:
     
    i)	Reference to the original object of the same class
    ii)	Does nothing by default ... FALSE used for Object instantiation (one reason I can think of)
    11) Print vector elements in a different function having only a print statement … is this correct?
    Code:
     for_each (myvector.begin(), myvector.end(),printVect);… this was one of the choices given
    Code:
    void printVect(int i) {  // function for printing vector elements
      std::cout << ' ' << i;
    }
    int main () {
    std::vector<int> myvector;
    // populate vector;
    
    for_each (myvector.begin(), myvector.end(),printVect);
    std::cout << '\n';
    }
    Can we do it with FOR LOOP?

    Thanks and Regards

  8. #8
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    Re: Online C++ Test Questions

    4)
    Code:

    Obj1 and Obj2 are the Objects of the same class (type)
    e-g if “Object” is the class name:
    Object obj1 = new Object();
    Object obj2;
    Obj2 = obj1 ........... do
    This is not valid c++ code. new returns a pointer which is tried to be assigned to a non-pointer instance of a class. The variable Obj2 does not exist (it should be obj2) and assuming obj1 is a pointer to an Object class, then obj2 also must be defined as a pointer variable.

    Given the revised code

    Code:
    #include <iostream>
    
    class Object {
    public:
    	int a;
    };
    
    int main()
    {
    Object *obj1 = new Object(); 
    Object *obj2;
    
    	obj2 = obj1;
    
    	std::cout << "address of obj1: " << obj1 << std::endl;
    	std::cout << "address of obj2: " << obj2 << std::endl;
    }
    then obj1 and obj2 do indeed point to the same memory address and hence to the same object.
    All advice is offered in good faith only. You are ultimately responsible for effects of your programs and the integrity of the machines they run on.

  9. #9
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    Re: Online C++ Test Questions

    Quote Originally Posted by gulHK View Post
    [/code]
    8) Default copy constructor does what
    Code:
     
    i)	Reference to the original object of the same class
    ii)	Does nothing by default ... FALSE used for Object instantiation (one reason I can think of)
    That is not what the answer should be. There is one universal answer, and that is to state what the default copy constructor does. I stated the answer in my previous post.

    Regards,

    Paul McKenzie

  10. #10
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    Re: Online C++ Test Questions

    Thank You Very Much 2Kaud.

  11. #11
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    Re: Online C++ Test Questions

    Thank You Very Much Paul.

  12. #12
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    Re: Online C++ Test Questions

    Quote Originally Posted by 2kaud View Post
    This is not valid c++ code. new returns a pointer which is tried to be assigned to a non-pointer instance of a class. The variable Obj2 does not exist (it should be obj2) and assuming obj1 is a pointer to an Object class, then obj2 also must be defined as a pointer variable.
    This is actually perfectly valid C++ assuming there is a constructor for Object that takes a Object* as parameter and that constructor isn't declared as explicit.
    Granted, it's rare you'd write such a constructor (and not declare it explicit if you do, it's accidents waiting to happen).
    Last edited by OReubens; September 20th, 2013 at 07:20 AM.

  13. #13
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    Re: Online C++ Test Questions

    Quote Originally Posted by OReubens View Post
    This is actually perfectly valid C++ assuming there is a constructor for Object that takes a Object* as parameter and that constructor isn't declared as explicit.
    Granted, it's rare you'd write such a constructor (and not declare it explicit if you do, it's accidents waiting to happen).
    Yep, those assignments can be made to be legal. I never figured on having an Object constructor that takes as argument Object *! I'll remember that one next time I ask some newbie c++ questions

    Code:
    #include <iostream>
    
    class Object {
    public:
    
    	Object()
    	{
    	}
    
    	Object(Object*)
    	{
    	}
    };
    
    int main()
    {
    Object *obj1 = new Object(); 
    Object *obj2;
    
    Object obj3 = new Object();
    Object obj4;
    
    	obj2 = obj1;
    	obj4 = obj3;
    
    	std::cout << "address of obj1: " << obj1 << std::endl;
    	std::cout << "address of obj2: " << obj2 << std::endl;
    	std::cout << "address of obj3: " << &obj3 << std::endl;
    	std::cout << "address of obj4: " << &obj4 << std::endl;
    }
    In this case the output is
    Code:
    address of obj1: 00323FF0
    address of obj2: 00323FF0
    address of obj3: 0012FEE0
    address of obj4: 0012FEE4
    which shows that obj1 and obj2 point to the same object and obj3 and obj4 point to different objects.
    All advice is offered in good faith only. You are ultimately responsible for effects of your programs and the integrity of the machines they run on.

  14. #14
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    Re: Online C++ Test Questions

    That's great. Thank you very much for explaining it with a practical example.

  15. #15
    Join Date
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    Re: Online C++ Test Questions

    Hello everyone

    Could anyone please help me with this online interview question?

    Code:
    Object1 and Object2 are the names of two different classes.
    The Class Object2 has one Object and the Class Object1 does not have any objects
     
    Object2 obj2 = new Object2();
    cout << dynamic_cast< Object1>(obj2) << endl; ....... what does this line print?
    Many Thanks

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