constructor and destructor
TRANSCRIPT
CONSTRUCTOR AND
DESTRUCTOR
1. Point out the errors, if any, in the following program.class date{
private:int day,month,year;
date(){
day = 2;month = 10;year = 2008;
}};
void main(){
date today;}
Error : The default constructor is defined under private section; so it is not
accessible in function main( ).
2. Point out the errors, if any, in the following program.class value{
private:int i;float f;
public:value(){
i = 0;f = 0.0;return 1;
}};void main(){
value vi;}
Error : The constructor should not return
any value. Here constructor contains return statement.
3. Read the following code segment.#include <iostream.h>class sample{
int x, y;public: sample(int a = 10, int b = 20) {
x = a;y = b;
} void show() {
cout << “\n x = “ << x << “y = “ << y; }
};void main(){
sample s1;sample s2(4);sample s3 = sample(6,8);s1.show();s2.show();s3.show();
}Explain the working of constructor for the creation of each object.What will be the output of the above code.
b) x = 10, y=20 x = 4, y=20 x = 6, y=8
4. A class named employee is having the following constructors.
i) employee();ii) employee(int, float);iii) employee(employee &f);
A) Name the category to which each constructor belongs.B) Write down the purpose of each.C) Define the destructor for this class.
1. i) default constructor, ii) parameterized constructor, iii) copy constructor2. short note about default constructor, parameterized constructor and copy constructor3. ~employee( ) { }
5. The following code defines a class for finding out the area of a circle.#include<iostream.h>class circle{
float rad;public:
circle(float x){
rad = x;}void area(){
cout << 3.14 * rad * rad;}
};void main(){
circle(5.5).area();}What is the purpose of the statement in the main function?What is the output?
a)Through this statement, an anonymous object (temporary instance) is created and initialized with the value 5.5 and that object calls the member function area( )b) 94.985
6. While declaration, initialization is possible with variables, arrays and structures. What about of classes? Justify your answer.
• But an object of a class cannot be initialized in similar fashion because the access labels restrict the accessibility of the data members.
7. A constructor is usually defined in public section. Why?
• Generally a constructor is defined under the public section of a class so that its objects can be created in any function.
8. Is constructor definition compulsory? Give justification to support your answer.
• Yes, constructor definition is compulsory. A Constructor is defined like other member functions of a class. It can be defined either inside or outside the class specification.
9. List down the characteristics of constructors. • They should be declared in the public section.• They are invoked automatically when the objects are
created.• They do not have return types, not even void and
therefore, and they cannot return values.• They cannot be inherited.• Like other C++ functions, they can have default
arguments.• They cannot be virtual.• We cannot refer to their addresses.• They cannot be static.
10. List down the characteristics of destructors. • They are invoked automatically when the objects are
destroyed.• They obey the usual access rules that other member
functions do.• They cannot be inherited.• No argument can be provided to a destructor, neither
does it return any value.• They cannot be virtual.• We cannot refer to their addresses.• They cannot be static.• If there is no destructor in a class, a default destructor is
generated by the compiler.