nomemory / cpp-interview-questions

C++ interview questions

• What is a reference ?
• What is the difference between pass-by-reference and pass-by-value ?
• What are the main differences between a struct and a class ?
• Are there any scenarios where you would normally use a struct over a class ?
• What are the main differences between a reference and a pointer ?
• What is polymorphism in C ?
• Explain the usage for the virtual keyword ?
• What is wrong with the following code:

class A
{
    public:
        A() {}
        ~A(){}
};

class B: public A
{
    public:
        B():A(){}
        ~B(){}
};

int main(void)
{
  A* a = new B();
  delete a;
}

Answer: Undefined behavior because A destructor is not virtual.

• What is the output:

unsigned char half_limit = 150;

for (unsigned char i = 0; i < 2 * half_limit; ++i)
{
    // do something;
}

Answer: Infinite Loop (overflow)

• Explain what the keyword static is doing ?
• What is the following:

#include <iostream>
#include <string>
using namespace std;
 
void demo() {
    static int count = 0;
    cout << count << " ";
    count++;
}
 
int main()
{
    for (int i = 0; i < 5; i++)
        demo();
    return 0;
}

• What is the O(n) for the following code ?

int main() {
  int n = 10; //n can be anything
  int sum = 0;
  float pie = 3.14;
  int var = 1;

  while (var < n){
    cout << pie << endl;
    for (int j=0; j<var; j++)
      sum+=1;
    var*=2;  
  }
  cout<<sum;
}

Answer is O(N)

Code questions