Classes and Objects : MCQs & PYQs with Explanation

Option A

In C++, a structure (struct) is similar to a class, but one key difference lies in the default access specifier. When you create a structure and define variables or functions inside it, those members are public by default.
While a class keeps its members private by default, meaning they cannot be accessed directly from outside unless specified.

Option A

An enum in C++ is a user-defined data type whose variables are internally stored as integers. The variable sh is declared as type enum suresh and assigned the value sir. 
When the sizeof(sh) expression is evaluated, it returns the size of the enum variable, not the number of elements in the enum. 
Since the question clearly states that an integer occupies 2 bytes of memory, and an enum variable uses the same memory size as an int, the result of sizeof(sh) is 2 bytes.

Option D

A class in C++ is a blueprint that can hold different types of members. Its main purpose is to group data and related functions together, but it can store many kinds of data, including arrays, simple variables, and functions.

Option B

In C++, memory that is allocated dynamically using the new keyword must be released using the delete keyword.

• The delete frees the memory allocated at runtime.
• It also calls the destructor of the object, if any.
• This helps prevent memory leaks.

E.g.:
int *ip=new int; // Dynamic Memory Allocation.
delete ip; // Release Allocated Memory.

Option D

In C++, a program can have multiple scopes, such as global scope, class scope, and local scope. Sometimes, the same name is used in different scopes. In such cases, the compiler needs a way to know which exact variable or function we want to access.
The :: operator, called the scope resolution operator, is used for this purpose. It tells the compiler to resolve the scope and access the member that belongs to a specific scope.

• To access a global variable when a local variable has the same name.
• To define or access a class member outside the class.
• To access members of a namespace.

E.g.:
int num=10;
int main() 
{
    int num=20;
    cout<<num; //Access local num.
    cout<<::num; //Accesses global num.
}

Option B

In C++, the member of class whether variables or functions are private by default. This is an important basic concept in Object-Oriented Programming because it helps in data hiding.

• Structure (struct), all members are public by default means accessible from anywhere.
• Class (class), all members are private by default means only accessible within the class.

struct Student
{
    int marks;
};
int main()
{
    Student s;
    s.marks=101;  // Works fine (public access).
    return 0;
}
class Student 
{
    int marks;
};
int main()
{
    Student s;
    s.marks=101;  // Compile time error (private access).
    return 0;
}

Option D

In C++, when a class is defined, no memory is allocated at that time. A class is only a blueprint or template that defines data members and member functions. Memory allocation happens only when an object of the class is created.
class Demo
{
    int p;
};
Demo myObj; // Memory is allocated here.

Option A

In C++, when a member function is defined inside the class definition, the compiler treats it as an inline function by default. This means the compiler may replace the function call with the actual function code to reduce function call overhead.
class Demo
{
    public:
    void display()
    {
        cout << "Hello from display()";
    }
};
Here, display() is considered an inline function.

Option A

A class is a blueprint, and an object is a real-world instance created using that blueprint. When you create an object of a class, you are creating an instance of that class, which holds the actual data.

Option B

In C++, class members functions can be declared inside the class but defined outside using the scope resolution operator ::. This operator tells the compiler that the function you are defining belongs to a specific class.
Syntax:
            Return_Type Class_Name :: Function_Name (Arguments);
class MyClass
{
public:
    void myFunction();  //Declaration inside class.
};
void MyClass::myFunction() //Definition outside class.
{
    // Function body.
}

#include<iostream.h>
#include<conio.h>
class first
{
	int a,b;
	public:
	void get();
	void show();
};
class second
{
	int x,y;
	public:
	void input()
	{
	     x=5; y=10;
	}
	void show();
};
void first::get()
{
    cout<<"Enter The Two Number: ";
    cin>>a>>b;
}
void first::show()
{
	cout<<"
Entered Number Is
";
	cout<<a<<endl<<b;
}
void second::show()
{
	cout<<"
In Class Second
";
	cout<<x<<endl<<y;

}
void main()
{       
	first f;
	f.get();
	f.show();
	second s;
	s.input();
	s.show();  
}

Option C

In C++, dynamic memory allocation is done using the new keyword on the heap. Memory allocated using new should be released using the delete keyword.
#include <iostream>
using namespace std;
int main() 
{
    int *p=new int;
    *p=22;
    cout<<"Value : "<<*p;
    delete p;
    return 0;
}
OUTPUT
Value : 22

Option B

In C++, a structure is similar to a class, but one key difference lies in the default access specifier. When you create a structure and define variables or functions inside it, those members are public by default.
While a class keeps its members private by default, meaning they cannot be accessed directly from outside unless specified.

• Structure (struct), all members are public by default means accessible from anywhere.
• Class (class), all members are private by default means only accessible within the class.

struct Student
{
    int marks;
};
int main()
{
    Student s;
    s.marks=101;  // Works fine (public access).
    return 0;
}
class Student 
{
    int marks;
};
int main()
{
    Student s;
    s.marks=101;  // Compile time error (private access).
    return 0;
}

Option C

In C++, the member of class whether variables or functions are private by default. This is an important basic concept in Object-Oriented Programming because it helps in data hiding.

• Structure (struct), all members are public by default means accessible from anywhere.
• Class (class), all members are private by default means only accessible within the class.

struct Student
{
    int marks;
};
int main()
{
    Student s;
    s.marks=101;  // Works fine (public access).
    return 0;
}
class Student 
{
    int marks;
};
int main()
{
    Student s;
    s.marks=101;  // Compile time error (private access).
    return 0;
}

Option B

In C++, access specifiers such as private, protected, public control how class members can be accessed.

• The public members can be accessed directly using an object of the class.
• The private members cannot be accessed directly outside the class. They are accessible only through member functions of the class.

Option B

In C++, both structures (struct) and classes (class) are used to group data and functions together. They are almost identical in functionality, but the main difference is in default access specifiers.
Structures (struct): By default, all members are public. This means they can be accessed directly from outside the structure.
Classes (class): By default, all members are private. This means they cannot be accessed directly from outside the class unless specified as public.