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C++ Practice Questions

Topics Covered:
C++ Variables, Data Types, Functions, Classes, Loops, STL, and more

30 Questions

Practice Questions

1. What will be the output of the following C++ code? 
#include 
using namespace std;
int main(){
    int i = 1;
    while(true){
        if(i % 3 == 0)
            break;
        cout << i << " ";
        i++;
    }
    return 0;
}
2. Which of the following symbols is used for single-line comments in C++?
3. What are the outputs of the following C++ code snippet? 
#include 
#include 
using namespace std;
int main(){
    cout << pow(2, pow(3,2)) << endl;
    cout << pow(pow(2,3),2) << endl;
    return 0;
}
4. What is the output of the following C++ code snippet? 
#include 
#include 
using namespace std;
int main(){
    map main_dict;
    auto insert_item = [&](const string &item){
        if(main_dict.find(item) != main_dict.end())
            main_dict[item] += 1;
        else
            main_dict[item] = 1;
    };
    insert_item("Key1");
    insert_item("Key2");
    insert_item("Key2");
    insert_item("Key3");
    insert_item("Key1");
    cout << main_dict.size();
    return 0;
}
5. Which of the following lambda expressions correctly returns true for negative numbers in C++?
6. What is the output of the following C++ code? 
#include 
using namespace std;
class Human {
public:
    string human_name;
    Human(string name): human_name(name) { }
    string getHumanName() { return human_name; }
    virtual bool isEmployee() { return false; }
};
class IBEmployee : public Human {
public:
    string emp_id;
    IBEmployee(string name, string id): Human(name), emp_id(id) { }
    bool isEmployee() override { return true; }
    string get_emp_id() { return emp_id; }
};
int main(){
    IBEmployee employee("Mr Employee", "IB007");
    cout << employee.getHumanName() << " " << employee.isEmployee() << " " << employee.get_emp_id();
    return 0;
}
7. Which function is traditionally used in C++ to obtain the current time (as a time_t value representing seconds since the Unix epoch)?
8. In C++ file I/O, which of the following should you check to ensure the file was successfully opened?
9. Which of the following statements about C++ namespaces is false?
10. Which of the following statements about std::pow in C++ is correct?
11. Which method is used to check if a std::vector is empty?
12. What is the output of the following C++ code? 
#include 
using namespace std;
class X {
  private:
    int num1;
  public:
    int num2;
    X(): num1(5), num2(2) { }
    void display_values() { cout << num1 << " " << num2; }
};
class Y: public X {
  private:
    int num1;
  public:
    Y(): X(), num1(1) { num2 = 6; }
};
int main(){
    Y obj;
    obj.display_values();
    return 0;
}
13. What is the key difference between std::vector and std::array in C++?
14. Which of the following statements about C++ constructors is false?
15. Given two vectors: vector<char> list1 = {'s','r','a','s'} and vector<char> list2 = {'a','a','n','h'}, what is the result of concatenating corresponding elements into a vector of strings?
16. Which C++ library is commonly used for object serialization?
17. Which STL algorithm can be used to count the number of elements in a vector that are multiples of 5?
18. What is the output of the following recursive C++ code? 
#include 
using namespace std;
int test(int x){
    if(x == 0)
        return 0;
    return x + test(x - 1);
}
int main(){
    cout << test(5);
    return 0;
}
19. Given vector<int> list1 = {3,4,5,2,1,0}, what is the content of list1 after performing list1.erase(list1.begin() + 1)?
20. Which build system is commonly used for C++ projects?
21. Consider the following C++ function with a default argument: 
#include 
#include 
using namespace std;
vector add_items(int x, vector items = vector()){
    items.push_back(x);
    return items;
}
int main(){
    vector a = add_items(1);
    vector b = add_items(2);
    // Suppose we print the contents of a and b.
    // What are the expected outputs?
    return 0;
}
(Assume that each call uses a fresh default value.)
22. Which of the following is the correct syntax for defining a function in C++?
23. What is the result of the expression 4 + 3 * 2 in C++?
24. Which of the following is NOT a characteristic of C++?
25. Which of the following declarations defines an immutable integer in C++?
26. What will be the output of the following C++ code snippet involving pointer arithmetic? 
#include 
using namespace std;
int main(){
    int arr[] = {10, 20, 30, 40};
    int *p = arr;
    cout << *(p + 2);
    return 0;
}
27. What is the maximum possible length of an identifier in C++?
28. What is the output of the following C++ code that uses a lambda with std::transform? 
#include 
#include 
#include 
using namespace std;
int main(){
    vector x = {0,1,4,9,16};
    vector y;
    transform(x.begin(), x.end(), back_inserter(y), [](int a){ return a + 2; });
    for(auto i : y)
        cout << i << " ";
    return 0;
}
29. Which of the following variable declarations defines a mutable integer in C++?
30. What will be the output of the following C++ code that uses a static variable? 
#include 
using namespace std;
void func(){
    static int count = 0;
    count++;
    cout << count << " ";
}
int main(){
    func();
    func();
    func();
    return 0;
}