Top 20 C & C++ Interview Questions

1. Define Storage Classes and explain application domain.

register - tell to the compiler for use a CPU register for fast aceess for that variable.

auto - it's a variable created and initialized when it is defined. It is not visible outside of the block.

static - defined inside of the function retain its value between calls. Always is initialized with 0. Defined as global in a file is visible on for the functions from that file.

extern - the definition of the variable is in another file.

2. Define the Storage Qualifiers

const - define a variable that can not change its value along the program execution.

volatile - define a variable that can be changed indirectly. An example can be a counter register that is updated by hardware.

mutuable - a member of a structure or object can be changed even if the structure, for example is declared const:

Ex: struct complex {mutuable int x; int y;};

const complex Mycomplex = {1, 2};

Mycomplex.x = 3; /* correct */

3. Give an example for a variable "const" and "volatile". Is it possible?

Yes, a status register for a microcontroller.

4. Detect if a linked list is circular.

Need to use 2 pointers, one incrementing by 1 and another by 2. If the list is circular, then pointer that is incremented by 2 elements will pass over the first pointer.

5. Have you any remarks?

#define res(a) a*a

Using in this form the result will not be like we expect. Thinking that "a" is replaced with (2+3), then we will obtain 2+3*2+3 = 11 instead (2+3)*(2+3) = 25.

Use always #define res(a) (a)*(a)

6. Define a "dangling" pointer

Dangling pointer is obtained by using the address of an object which was freed.

7. Any difference between "const int*ptr" and int *const ptr" ?

Yes, it's a major difference. First define a constant data and second define a constant pointer.

8. What is the declaration and definition of a variable?

The definition contains the implementation for a method or variable declaration. This is just an example.

9. Give a solution for a stack overflow situation.

func_call() {

funct_call();

}

Every time the above function is called the return address is stored onto the stack. Calling in this infinite loop will cause a stack overflow.

10. Give 4 examples for an infinite loop.

a. while (1) {}

b. for (;;) {}

c. do {}while{1};

d. label:

goto label;

11. Define Encapsulation

Part of the information can be hidden about an object. Encapsulation isolates the internal functionality from the rest of the application.

12. Define Inheritance

One class, called derived, can reuse the behavior of another class, known as base class. Methods of the base class can be extended by adding new proprieties or methods.

13. Define Polimorfism

A function having the same name, but different type or number of arguments.

Ex: The below functions can be members of the same class.

void calc(int a, int b);

void calc(float a, float b);

14. Define Constructor, Default Constructor and Copy Constructor

Constructor is used for creating and initializing an object.

Default Constructor has no arguments and is created by default if no explicit definition is used.

Copy Constructor is used for initializing the member variables with the values of another object of the same class.

Important: Copy Constructor is by default called when an object is returned from a function or when the object is passed as argument by value.

15. Define the differences between malloc/free and new/delete.

malloc() - allocate memory in the heap, but don't call the object constructor; unlike new().

new() and delete() - called for objects: construct and destruct its.

16. Define the standard prototypes for main() function

a. int main (void)

b. int main (int argc, char **argv)

c. int main (int argc, char *argv[])

17. What is destroyed in the following code?

Obj *ptr = new Obj[5];

delete ptr;

Only the first element of the Obj[5] vector is deleted because ptr is pointing to the first element of the array.

18. What is a virtual function?

A derived class may use the redefinition for a function from the base class. To be possible, need to declare that function virtual in the base class.

19. What is an inline function?

It's a directive for the compiler which says that the code of the function is used every time we have a call. In this way are avoided the jump to the function routine and return. Inline function needs to be small.

20. Explain the public, private and protected access specifies.

public - data and methods can be accessed outside of the object class.

protected - data and methods are available only for derived classes.

private - data and methods can not be accessed outside of the object class.