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September 19th, 2013, 10:16 AM
#1
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 ...13) Rough Code
Code:
Pointer1 ptr1 = new Pointer;
Pointer2 ptr2;
ptr2 = ptr1; ..... how to assign? Syntax
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September 19th, 2013, 10:51 AM
#2
Re: Online C++ Test Questions
Originally Posted by gulHK
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
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September 19th, 2013, 11:22 AM
#3
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 ...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.
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September 19th, 2013, 01:13 PM
#4
Re: Online C++ Test Questions
Originally Posted by gulHK
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
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September 19th, 2013, 01:36 PM
#5
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. All my code is tested (unless stated explicitly otherwise) with the latest version of Microsoft Visual Studio (using the supported features of the latest standard) and is offered as examples only - not as production quality. I cannot offer advice regarding any other c/c++ compiler/IDE or incompatibilities with VS. You are ultimately responsible for the effects of your programs and the integrity of the machines they run on. Anything I post, code snippets, advice, etc is licensed as Public Domain https://creativecommons.org/publicdomain/zero/1.0/ and can be used without reference or acknowledgement. Also note that I only provide advice and guidance via the forums - and not via private messages!
C++23 Compiler: Microsoft VS2022 (17.6.5)
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September 19th, 2013, 01:45 PM
#6
Re: Online C++ Test Questions
Originally Posted by 2kaud
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.
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September 19th, 2013, 03:59 PM
#7
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
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September 19th, 2013, 05:35 PM
#8
Re: Online C++ Test Questions
Originally Posted by gulHK
[/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
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September 20th, 2013, 02:15 AM
#9
Re: Online C++ Test Questions
Thank You Very Much Paul.
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September 19th, 2013, 04:52 PM
#10
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. All my code is tested (unless stated explicitly otherwise) with the latest version of Microsoft Visual Studio (using the supported features of the latest standard) and is offered as examples only - not as production quality. I cannot offer advice regarding any other c/c++ compiler/IDE or incompatibilities with VS. You are ultimately responsible for the effects of your programs and the integrity of the machines they run on. Anything I post, code snippets, advice, etc is licensed as Public Domain https://creativecommons.org/publicdomain/zero/1.0/ and can be used without reference or acknowledgement. Also note that I only provide advice and guidance via the forums - and not via private messages!
C++23 Compiler: Microsoft VS2022 (17.6.5)
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September 20th, 2013, 02:15 AM
#11
Re: Online C++ Test Questions
Thank You Very Much 2Kaud.
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September 20th, 2013, 07:17 AM
#12
Re: Online C++ Test Questions
Originally Posted by 2kaud
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.
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September 20th, 2013, 07:57 AM
#13
Re: Online C++ Test Questions
Originally Posted by OReubens
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. All my code is tested (unless stated explicitly otherwise) with the latest version of Microsoft Visual Studio (using the supported features of the latest standard) and is offered as examples only - not as production quality. I cannot offer advice regarding any other c/c++ compiler/IDE or incompatibilities with VS. You are ultimately responsible for the effects of your programs and the integrity of the machines they run on. Anything I post, code snippets, advice, etc is licensed as Public Domain https://creativecommons.org/publicdomain/zero/1.0/ and can be used without reference or acknowledgement. Also note that I only provide advice and guidance via the forums - and not via private messages!
C++23 Compiler: Microsoft VS2022 (17.6.5)
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September 20th, 2013, 09:05 AM
#14
Re: Online C++ Test Questions
That's great. Thank you very much for explaining it with a practical example.
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September 21st, 2013, 06:18 AM
#15
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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