Prerequisite – Constructors in C++

1. What is the output of following program?
   
   

   
   
   

   #include <iostream> using namespace std;    class construct {      int a, b; public:      construct()     {         a = 0;         b = 0;     } };    int main() {     construct c;     cout<< "a: "<< c.a << endl << "b: "<< c.b;     return 1; }

   Output:

   error
     

   Description: The variables in the class are by default private in C++. And therefore, they cannot be accessed out side the class. For the code, to work perfectly they need to be declared as public like the construct() then it will print a and b as 0.

2. What is the output of following program?
   
   

   
   
   

   #include <iostream> using namespace std;    class construct {     public:     float area;                  construct()     {         area = 0;     }            construct(int a, int b)     {         area = a * b;     }            void disp()     {         cout<< area<< endl;     } };    int main() {     construct o;     construct o2( 10, 20);     o.disp();     o2.disp();     return 1; }

   Output:

     0
     200
   

   Description: C++ allows more than one constructor. The other constructors must have different parameters. Additionally, constructors which contain parameters are given default values must adhere to the restriction that not all parameters are given a default value. This is a situation which only matters if there is a default constructor.The constructors get loaded when an object is created based on the parameters.

3. Which constructor will be executed?
   
   

   
   
   

   #include<iostream> using namespace std;     class constructor {     int x, y;      public:     constructor(int a = 10, int b = 20 )     {         x = a;          y = b;     }     void Display()     {         cout<< x << " " << y << endl;     }  }; int main() {     constructor objBix;      objBix.Display();      return 0; }

   Output:

    default constructor
     

   Description: Here, a parameterised constructor is declared but the object corresponding to that constructor is not created. Therefore, only Default constructor is executed and the control is passed to the function at the function call.

4. What is the output of following program?
   
   

   
   
   

   #include<iostream.h>  class constructor {     int x;      public:     constructor(short ss)     {         cout<< "Short" << endl;     }     constructor(int xx)     {         cout<< "Int" << endl;     }     constructor(float ff)     {         cout<< "Float" << endl;     } }; int main() {     constructor c('B');     return 0;  }

   Output:

   
   
   
   

   Int
     

   Description: As ‘B’ gives the integer value i.e, 66. so, the parameterized constructor with integer parameter will be executed.

5. What is the output of following program?
   
   

   
   
   

   #include <iostream> using namespace std;    class constructor  {     int a;   public:     constructor(int x)     {         a = x;     }            void display()     {         cout<< "a: "<<a << endl;     } }; int main() {      constructor c1(10);    constructor c2 = c1;    c1.display();    c2.display();    return 1; }

   Output:

   a: 10
   a: 10
     

   Description: This program demonstrates copy constructor concept.

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